Comment function generic_checkout_git.
Make is_truenas a function so we can avoid dup code.
Support for building "nas_ports" directly from source.

If NAS_PORTS_DIRECT or NAS_PORTS_DIRECT_SYSUTILS_ZFSD is
defined, then we expect to find sources in
/usr/ports/nas_source/zfsd to build our project.

Otherwise we fetch a distfile.
Follow convention of GIT_$proj_REPO.
WIP, support for ADDL_REPOS
Fix mount of nas_source for nas_port build.
Don't set 'extract' target to NULL.

'extract' is needed to make WRKDIR, just set EXTRACT_ONLY to NULL
to not extract anything.
Pass through NAS_PORTS_DIRECT into ports build.

also pass through NAS_PORTS_DIRECT_${CATAGORY}_${PORT}
"all" target -> "obj all", fixes MAKEOBJDIRPREFIX

Turn off parallel build via MAKE_JOBS_UNSAFE to also fix
mkdir of MAKEOBJDIRPREFIX.
Explicitly set MAKEOBJDIRPREFIX for nas_ports.
Don't clean by default, we want obj directories.

Mark the rm-rf that nukes other object files with XXX as
it may soon be removed.
Use -DNO_KERNELCLEAN when building debug kernel.

This saves about 1m30s off the build.
Use a local distcache for our files by default.

This is safe and sane for !iX developers.  Other developers
are encouraged to set MASTER_SITE_OVERRIDE to their own local
cache.
comment the background fetch programs
turn off debug
fix error with missing newline causing vars to be missed.
cd into sandbox build dir, advise to run 'make checkout'
make nas_source if it does not exist