Downstream clients sometimes want to use a custom Python "binary" stub script that loads up their own library code, a specific fabfile, or does other bookkeeping-y things prior to calling Fabric. In these situations they typically do still want to expose Fabric's CLI API at the end of the run (and/or don't want to force users to always call fab -f /path/to/fabfile.)
fab -f /path/to/fabfile
Unfortunately, fabric.main.main() is un-parameterized and it's not possible to even pass in a specific fabfile.
This would be a small change that makes things more flexible for some users, without requiring us/me to totally rearchitect main.py.
Parameterize main.main() for explicit fabfile locations.
Changelog re #761