Revert "repo rework: Re-add compatibility url field"
Revert "repo rework: Remove stubs; Breaks repo compat."
Revert "repo rework: Remove need for repos to be self-aware"

This reverts commit a2b2f4d6427914cdcdb59943dd8e4a0bfdcd53ee.
This reverts commit 602076ef82647a48fd10f4d1ec830bb4242f9eb6.
This reverts commit 5ffaf72c8a74a7eb6827e4d2b1f47c9360ddaefe.

These changes break the build on Haiku and the ability to create repo
mirrors, for the lack of a replacement for the URL (an UUID was evoked
on the mailing lists, but not implemented).

We are due for a release soon, please don't break the build.

repo rework: Remove need for repos to be self-aware

* See #12917 for details.
* Squashed to one commit to make revert easy if we
run into any issues.
* pkgman is now pre-attached to the 'current' repo
version within nightly images so they can be updated
by default.
* This shouldn't impact us keeping older sets of package
versions by commit hash for building older hrevs.
* There are XXX stubs with "Kill me". These will need
to be dropped after users are given sufficent time to
upgrade. We're dropping a previously required field (url)
so making this a slowish roll out.
* Makes the repos a lot less restrictive which should
help PM package building automation be a bit easier.
* Once this stuff smooths out, we'll add UUID's to the
repo definitions for duplicate repo detection.

Add HOST_LIBSUPC++ to fix compilation on MacOS X

Refactor reusable pkgman code into libpackage

* Move RepositoryBuilder class to libpackage and add B* prefix to name.
* Pull BPackageManager class out of PackageManager and move to
libpackage. The base class is customizable via three handler objects
responsible for transaction handling, request execution, respectively
user interaction.
* Reorganize _ApplyPackageChanges(): Now we first prepare the
transactions for all affected installation locations (downloading
files etc.) and then commit them.

Switch build system from optional package to repositories

* Build libsolv and the dependency solver part of the package kit for
the build platform.
* Add build tool get_package_dependencies. Given a list of package files
and a list of repository files it determines the additional packages
that need to be retrieved from the repositories and prints their URLs.
* Add rules to work with external repositories in the build system
(build/jam/RepositoryRules):
- PackageRepository declares an external repository with all its
packages. The URL of the repository file isn't specified. It is
computed from a given base URL and the SHA256 hash of the list of
package files.
- GeneratedRepositoryPackageList generates a file containing the file
names of all packages in a repository.
- IsPackageAvailable returns whether a package is available in any
repository.
- PackageURL returns the URL for a package.
* Declare the HaikuPorts repository for x86_gcc2
(build/jam/repositories/HaikuPorts/x86_gcc2).
* Add rule AddHaikuImagePackages to add a package to the image and rule
IsHaikuImagePackageAdded to determine whether a package has been
added.
* OptionalPackages: Remove all entries that just downloaded and
installed an external package. AddHaikuImagePackages can be used
instead and is used in the remaining entries. Also move the remaining
optional package dependency declarations from
OptionalPackageDependencies here.
* ExtractBuildFeatureArchives: Instead of the URL parameter a package
name must be specified now. This allows to simplify BuildFeatures
significantly, since there's no dealing with URLs anymore. "if" out
the entries that aren't supported yet.
* build_haiku_image: For the packages installed in system and common
resolve their dependencies and download and install them as well.

Add HOST_LIBSUPC++ to fix compilation on MacOS X

Refactor reusable pkgman code into libpackage

* Move RepositoryBuilder class to libpackage and add B* prefix to name.
* Pull BPackageManager class out of PackageManager and move to
libpackage. The base class is customizable via three handler objects
responsible for transaction handling, request execution, respectively
user interaction.
* Reorganize _ApplyPackageChanges(): Now we first prepare the
transactions for all affected installation locations (downloading
files etc.) and then commit them.

Switch build system from optional package to repositories

* Build libsolv and the dependency solver part of the package kit for
the build platform.
* Add build tool get_package_dependencies. Given a list of package files
and a list of repository files it determines the additional packages
that need to be retrieved from the repositories and prints their URLs.
* Add rules to work with external repositories in the build system
(build/jam/RepositoryRules):
- PackageRepository declares an external repository with all its
packages. The URL of the repository file isn't specified. It is
computed from a given base URL and the SHA256 hash of the list of
package files.
- GeneratedRepositoryPackageList generates a file containing the file
names of all packages in a repository.
- IsPackageAvailable returns whether a package is available in any
repository.
- PackageURL returns the URL for a package.
* Declare the HaikuPorts repository for x86_gcc2
(build/jam/repositories/HaikuPorts/x86_gcc2).
* Add rule AddHaikuImagePackages to add a package to the image and rule
IsHaikuImagePackageAdded to determine whether a package has been
added.
* OptionalPackages: Remove all entries that just downloaded and
installed an external package. AddHaikuImagePackages can be used
instead and is used in the remaining entries. Also move the remaining
optional package dependency declarations from
OptionalPackageDependencies here.
* ExtractBuildFeatureArchives: Instead of the URL parameter a package
name must be specified now. This allows to simplify BuildFeatures
significantly, since there's no dealing with URLs anymore. "if" out
the entries that aren't supported yet.
* build_haiku_image: For the packages installed in system and common
resolve their dependencies and download and install them as well.