revert: move bulk of revert command from commands to cmdutil This revision has no functionality change. The code on the original commands.revert() function has been split. The first part of the original code, which checks that the command inputs are correct remains in commands.revert(). The rest of the function, which performs the actual revert operation has been moved into cmdutil.revert(). The purpose of this change is to make it easier to perform a revert operation, from other parts of the code. This may be used to implement reverting of subrepos.