topic: support --rev argument and properly process then as user input Revisions inputed by the users should be processed using `scmutil.revrange`. This will take alias into account and allow extensions to monitor the user inputs. As a side effect, the '_changetopics' function takes revisions as argument. make the API clearer.

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null