revset: implement match() in terms of matchany() match() is the special case of a single element list being passed to matchany() with the additional error checking that the revset spec is defined. Change the implementation to remove the redundant code and have match() call matchany().

scmutil: improve documentation of revset APIs I can never remember the differences between the various revset APIs. I can never remember that scmutil.revrange() is the one I want to use from user-facing commands. Add some documentation to clarify this. While we're here, the argument name for revrange() is changed to "specs" because that's what it actually is.