This adds support of the new class state.statecheck
throughout core and extensions. This also removes the
previous method cmdutil.unfinishedstates and its API.
The results are shown in tests.
@martinvonz Doing that would be kind of difficult because these changes are not due to refactoring but due to statecheck.hint() which is a unified function for generating hint messages. If I change the messages in accordance to cmdutil.unfinishedstates then this problem will be there in the in integration of STATES. If you still want it I can do that by removing statecheck.hint() completely and getting the messages from cmdutil.py. So should I do that ?