Before this patch, if hidden changesets were specified (e.g. with

--revision-range), rbtools would fail because Mercurial would complain

about changesets not being found. Mercurial "pretends" it doesn't know

about hidden changesets unless --hidden is specified.
This patch adds --hidden to all Mercurial commands that could interact

with hidden changesets. If the current Mercurial install doesn't support

hidden changesets (this is detected at run time), this argument is

stripped before command execution.
An alternative to this implementation would require the user to pass

--hidden to rbtools or would require the user to activate hidden

changeset support in the rbtools config. It is the opinion of this patch

author that things should "just work" and the user shouldn't be required

to do anything special to get rbtools to play nice with hidden

changesets.

Manually testing diff --revision-range with hidden changesets.