Support for MacPorts (incomplete -- checkpoint)

ref: wayneeseguin/rvm#1555
Support for Fink (very preliminary -- checkpoint)

ref: wayneeseguin/rvm#1555

note: only simple substitution, so far, based on mpapis's brew script
Support for Fink (incomplete -- checkpoint)

ref: wayneeseguin/rvm#1555
Merge github.com:baburdick/rvm, closes #1618

Conflicts:
	scripts/functions/requirements/osx_port