Added functions for changing the filesystem "root" via an environment variable
Migrated my addons to libmaya

- headers have been merged
- introduced macro guards to allow for easy enabling and disabling (see usrsetup.h for these addons)
running (options) will now show enabled maya features
Reworked the file system stubbing so that the related GenOpen functions are the
only targets.

- This will make the number of places I need to stub out very small
- I also eliminated any functions in fsoverride that go through the GenOpen
functions as they are no longer necessary.
Finished adding support for file system rooting