FreeNAS Code

Add a -f src option to just do a rebuild of buildkernel and buildworld.

Requested-by: jpaetzel

Typo.

1. Implement -f ports; this is a short term implementation,
and once this has been pushed into nanobsd, it should go
there..
2. Add properly documented, pull sources only option.

Compress all csup transmissions to save bandwidth.

Turns out this the patch+append issue isn't a FreeNAS specific
problem. This is a csup bug as it properly deletes .c and .h
files.

Document appropriately.

Fix incremental builds for good.

The observation made is that all newly created files have a
corresponding .orig file with size 0. So nuke the newly
file the file to allow for repeatable, incremental builds.
This will allow someone to actually invoke arguments with
-f [all|ports] properly, regardless of the target file
mime-type.

Minor improvements:
1. Use complete test-mkdir style to improve readability.
2. Don't suffix paths with ${root} after we've cd'ed for
consistency and readability.

More do_build.sh improvements/corrections:

1. We only need to to mkdir ${root}/FreeBSD; csup takes care of the rest of the
directories.
2. Patching in new files doesn't work today with repeated builds when using
csup to pull files. It automatically appends to the previously created
file, which breaks the build in many cases as the function/label symbols
are defined multiple times. A proper fix is underway, but for now make
rebuilding pull new sources every time.

Improve/correct the top-level build script. In particular:
1. Fix the optimization which assumes that if the obj
directory is present then buildworld/buildkernel will
not need to be run. That is false if you provided the
-f option in the past, and as such would just generate
bogus images lacking new src features/patches.
2. Provide fine grained tuning of -f ports|all.
Rebuilding/not rebuilding ports has no effect today,
but it will in the future.
3. Print out a simple error message at the end if the
nanobsd build failed because nanobsd is extremely
quiet when things fail (except in terms of the exit
code).
4. Add a usage message and simple examples.
5. Update documentation.

Make forcing updates easier to grok and document them.

- Clean up the locking code.
- Add ContextSuite support.
- Document it.

Unittests coming sometime in the near future (manual
testing passed).