Fix removing dependencies on package removal

The dependencies must also be dissociated from the resolvables they have
been resolved to.

Optional dependency resolution tracing

Fix adding order dependent dependency resolution

PackageFSRoot::_AddPackage(): When adding a resolvable which isn't known
yet, make sure all already added matching dependencies are resolved.

Resolve dependencies to resolvables

WIP towards dependency package links

* Add ResolvableFamily and DependencyFamily classes for grouping equally
named resolvables/dependencies.
* Add hash tables to PackageFSRoot to track resolvables and
dependencies. That is done in {Add,Remove}Package.
* Resolvable does now have a list of Dependency objects, the ones it
satisfies.

Add Node::Init() flags parameter

* Add Node::Init() flags:
- NODE_FLAG_KEEP_NAME: Take over ownership of the name.
- NODE_FLAG_CONST_NAME: Don't copy the name -- it's a constant that
lives at least as long as the object.
* Remove Init() implementations in derived classes that just call the
base class version.

Move PackageFamily table to PackageLinksDirectory

Add yet empty package-links directory

* Add PackageLinksDirectory Directory subclass. Currently not doing
anything.
* PackageFSRoot: Create a PackageLinksDirectory.
* Volume: Add/remove the package links directory for the system volume.

WIP towards packagefs package links support

* Introduce Version class representing a version.
* Introduce Dependency and Resolvable class and add lists of either to
Package.
* Parse package attributes and add dependencies and resolvables to
Package.
* Add a mount type to Volume and add a respective mount parameter
"mount-type" (values "system", "common", "home", "custom"). Also
implies the shine-through type, if that's not given.
* Introduce class PackageFamily which groups equally named and versioned
packages.
* Add class PackageFSRoot. Each instance represents a possible file
system root (separate roots for different chroot environments). Tracks
Volumes belonging to the same root and their packages.

Fix removing dependencies on package removal

The dependencies must also be dissociated from the resolvables they have
been resolved to.

Optional dependency resolution tracing

Fix adding order dependent dependency resolution

PackageFSRoot::_AddPackage(): When adding a resolvable which isn't known
yet, make sure all already added matching dependencies are resolved.

Resolve dependencies to resolvables

WIP towards dependency package links

* Add ResolvableFamily and DependencyFamily classes for grouping equally
named resolvables/dependencies.
* Add hash tables to PackageFSRoot to track resolvables and
dependencies. That is done in {Add,Remove}Package.
* Resolvable does now have a list of Dependency objects, the ones it
satisfies.

Add Node::Init() flags parameter

* Add Node::Init() flags:
- NODE_FLAG_KEEP_NAME: Take over ownership of the name.
- NODE_FLAG_CONST_NAME: Don't copy the name -- it's a constant that
lives at least as long as the object.
* Remove Init() implementations in derived classes that just call the
base class version.

Move PackageFamily table to PackageLinksDirectory

Add yet empty package-links directory

* Add PackageLinksDirectory Directory subclass. Currently not doing
anything.
* PackageFSRoot: Create a PackageLinksDirectory.
* Volume: Add/remove the package links directory for the system volume.

WIP towards packagefs package links support

* Introduce Version class representing a version.
* Introduce Dependency and Resolvable class and add lists of either to
Package.
* Parse package attributes and add dependencies and resolvables to
Package.
* Add a mount type to Volume and add a respective mount parameter
"mount-type" (values "system", "common", "home", "custom"). Also
implies the shine-through type, if that's not given.
* Introduce class PackageFamily which groups equally named and versioned
packages.
* Add class PackageFSRoot. Each instance represents a possible file
system root (separate roots for different chroot environments). Tracks
Volumes belonging to the same root and their packages.