Update mono, F#: support "select"

[Luc Bourhis]

Hi,

I am writing an update for the fsharp port (F# language), which is very outdated. This requires an update to the mono port, from version 3 to 4. One could make the case to support every x.y version of Mono and F# as MacPorts does for python, ruby, etc and then to let the user choose with port select. I would appreciate some pointers on how to support “port select” though. 

Best wishes,

Luc J. Bourhis