[PATCH 0 of 1 rfc] Update -C on git and svn subrepos

[Erik Zielke]

This patch tries to make Subversion and Git subrepositories behave in
a way more similar to Mercurial subrepositories, when the main
repository is updated with update --clean.

So it try to call svn and git commands to get a similar result, I do
however think that there might be better commands to
call. E.g. because the git one is a little different.

Furthermore I am also wondering whether there isn't a better
way to figure out that a clean should be performed.