we now detect inconsistent modes, binding names, and various other errors.
typeck/trans integration is mostly done.
borrowck not so much.
more tests needed.
resolve3 wasn't checking this. Added test cases. Also added a helpful informational
message in the case where you have a variable binding that you probably think
refers to a variant that you forgot to import.
This is easier to do in resolve than in typeck because there's code in typeck
that assumes that each of the patterns binds the same number of variables.
