revset: make repo.anyrevs accept customized alias override (API)
Previously repo.anyrevs only expand aliases in [revsetalias] config. This
patch makes it more flexible to accept a customized dict defining aliases
without having to couple with ui.
revsetlang.expandaliases now has the signature (tree, aliases, warn=None)
which is more consistent with templater.expandaliases. revsetlang.py is now
free from "ui", which seems to be a good thing.