Detect unsupported platforms

Detect unsupported platforms and try to help the user, if there is
something they can do about it.

For example, not every JRuby mode is unsupported, we can guide the user
what to do to enable support for that platform.

@guilleiguaran, @ryandao do you guys have any feedback? I tried not to
over engineer the solution and let it happen require time. If you have other
ideas or want to reword the messages, I'll be quite grateful :)