[PATCH 0 of 2 rfc] Sticky subrepos

[Erik Zielke]

This patch series consists of two patches. The first patch in the
series has been sent before.

Patch 1 tries to make handling of update -C more similar for the three
different kinds of subrepositores [hg, svn, git].

Patch 2 introduces sticky subrepositories.

Sticky subrepositories are that the subrepositories stay at the
version they are checked out in, if it is not the same as the version
recorded in .hgsubstate and there is no changes in the subrepository.
If the version checked out has changed then a warning is printed, that
the subrepository will not be updated to a different revision, and a
hint depending on whether there have been changes on top of that.  I
am not sure what the hint should be for svn and git subrepositories
and I also think the hints for hg subrepos could be improved.