errors: raise InputError from revpair() iff revset provided by the user
Same reasoning as for `revrange()` in an earlier patch.
Differential Revision: https://phab.mercurial-scm.org/D11561
# name space package to host third party extensionsfrom__future__importabsolute_importimportpkgutil__path__=pkgutil.extend_path(__path__,__name__)