First attempt to restore the rebase
First attempt to restore the rebase

Added a join_method flag, currently set to merge.
If you change this flag into rebase you will try the
new embryo of rebase functionality.
No tests written yet for this, only manually tested.
With join_method as merge everything works as usual.

ingydotnet/git-subrepo,perlpunk/git-subrepo,ingydotnet/git-subrepo,perlpunk/git-subrepo