[PATCH 1 of 2 stable] tests: add test for rebasing merges with ancestors of the rebase destination

[Pierre-Yves David]

Simple baseline:

   Merges may contains valuable information, rebase is never going to 
drop them.

You can search for improvement inside theses rule. I'm going to reject 
any solution that drop merges because they are merge.

In my opinion, the search for this solution starts with a proper wording 
of the problem you face and the various element involved. I'm not going 
to trust your solutions until I trust your analysis.

Cheers,

-- 
Pierre-Yves David