Implicit DNX min version check

[muratg]

If any of the packages in project.json depend on a particular DNX and this is not less than the DNX version we're currently using, we can detect and throw on the app start. This would prevent some of the issues described in this bug: dotnet/aspnetcore#312 (comment)

[davidfowl]

@muratg I think we need to do this for beta6

[muratg]

@victorhurdugaci has found a potential issue that we'll need to discuss. Tentatively putting in beta 6.

[davidfowl]

Reopening this /cc @muratg @glennc

[analogrelay]

/cc @avanderhoorn (I think this is what you were talking about ;)). Only covers one direction (packages later than runtime) though.

[avanderhoorn]

@anurse thanks, better than nothing!

[victorhurdugaci]

• Check for the version of Abstractions
• If the app tries to load a newer one, stop it