[PATCH 0 of 4 ] revert: add support for reverting

[Angel Ezquerra]

The first patch refactors the revert function on the commands module,
moving most of its code into cmdutil.revert.

The second and third patches add support for reverting modified subrepos.

The last patch is the one I'm most unsure about.
It adds support for reverting added subrepos. It is based on
automatically modifying the .hgsub and .hgsubstate files. I'm not sure
that is the best approach.