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.

checkheads: handle partial obsolescence We now properly detects situations were only parts of the remote branch is obsoleted. To do so, we process children in the branch recursively to see if they will be obsolete. The current code has some trouble when the remote branch in unknown locally, or when the prune happened on a successors that is not relevant to the push. These case will be handled later. The processing code is becoming more and more complex, a lighter approach would be to check for the obsolescence markers that are relevant to the pushed set, but I prefer to stick with the current approach until more test cases are written.

test: force a push in inhibit's test Our checkheads detection code is becoming better and will prevent that push. As we do not care about this for inhibit, we simply force the push.

checkheads: basic handling of pruned heads (and associated tests) We now detect that heads was pruned and stop warning about it. Note that this has the same shortcoming as the existing code and only looks at the heads.

checkheads: give up on processing locally unknown changeset There are too many issue with locally unknown changesets, we ignore them for now while we get the core feature of the detection working.

checkheads: import our own copy of the checkheads code I expect enough change and experimental will be made that is it worthwhile having them done in evolution close to the rest of the exchange tests make sense.

compat: work around some filecache bug in 3.8 We are still compatible with this version.

obshashrange: have an half descent wireprotocol command The previous implementation was extremely hacky. The new version is based on the other discovery function and work!