checkheads: add more complexe case where a branch is split on multiple ones We extend case A-6 and A-7 with partial counterpart. These case are interesting because some of the partial pushing will (rightfully) works and some other won't.

checkheads: add a test of partially pushing a branch spread on multiple other If a branch is fully obsolete but is result are spread on multiple branch, pushing only one of them should detect we create new branches.

checkheads-tests: add missing parents recording for prune markers It is a bit too easy to forget about theses :/ If they are missing, the markers are not going to be exchanged on push.

checkheads: add some extra tests about "partial push" This adds a couple of test that checks that the head replacement code is properly ignored replacement not relevant to the push.