evolvestate: rename the file to state.py and class name to cmdstate The evolvestate.py and the evolvestate class in it were introduced to help `hg evolve` grow continue and abort options. But the class and it's API can be easily used to store state information for other state files like we stored the information for grab state in the previous commit. Let's rename the the file and class.

branching: merge with stable

update: show "use 'hg evolve' to..." hint iff evolve command enabled Before this patch, one had to enable *all* commands (by including "allnewcommands" in the experimental.evolution config) for the hint to be shown.