Move source files out of the build directory and into a src/freenas
directory.  These source files do not conflict with other files
in the FreeBSD base system installed by "make installworld".

Add these files in the freebsd/src directory to the freenas-files package,
by modifying the appropriate Makefile and pkg-plist.

This will make packaging the base OS a little easier.
Remove the add_warden_hooks build step.
These files are now added via the freenas-files package.
Change to INSTALL_DATA for sudoers file.