MFC r314655:

bin: normalize paths using SRCTOP-relative paths or :H when possible

This simplifies make logic/output

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Merge the projects/release-pkg branch to head.

This allows packaging the base system with pkg(8), including
but not limited to providing the ability to provide upstream
binary update possibilities for non-tier-1 architectures.

This merge is a requirement of the 11.0-RELEASE, and as such,
thank you to everyone that has tested the project branch.

Documentation in build(7) etc. is still somewhat sparse, but
updates to those parts will follow.

Sponsored by: The FreeBSD Foundation

Switch the default WARNS level for sbin/ to 6.

Submitted by: Ulrich Spörlein

Bring mount_nullfs up to WARNS=6.

style.Makefile(5):
Use WARNS?= instead of WARNS=.

Default to WARNS=2.
Binary builds that cannot handle this must explicitly set WARNS=0.

Reviewed by: mike

Rename (after a repo-copy) some mount(8) programs:

mount_fdesc -> mount_fdescfs
mount_null -> mount_nullfs
mount_portal -> mount_portalfs
mount_umap -> mount_umapfs
mount_union -> mount_unionfs

- FDESC, FIFO, NULL, PORTAL, PROC, UMAP and UNION file
systems were repo-copied from sys/miscfs to sys/fs.

- Renamed the following file systems and their modules:
fdesc -> fdescfs, portal -> portalfs, union -> unionfs.

- Renamed corresponding kernel options:
FDESC -> FDESCFS, PORTAL -> PORTALFS, UNION -> UNIONFS.

- Install header files for the above file systems.

- Removed bogus -I${.CURDIR}/../../sys CFLAGS from userland
Makefiles.

- Backout botched attempt to introduce MANSECT feature.
- MAN[1-9] -> MAN.

Set the default manual section for sbin/ to 8.

Removed definition of _NEW_VFSCONF. The new vfsconf interface is now
the default.

Merge from Lite2 (use new getvfsbyname() and mount(2) interface)

This time: an absolute -I :-<

Convert to our man installation style. Also fixed long-standing bug
in `fastboot'/`fasthalt' in which the interpreter would hang around
after `reboot' or `halt' is run, causing an irritating ``Killed'' message.

BSD 4.4 Lite sbin Sources

Note: XNSrouted and routed NOT imported here, they shall be imported with
usr.sbin.