compat: fix obslog compatiblity with 4.3 Due to the way of how successor sets are retrieved in new Mercurial version, retrieving it again in 4.3 way would be a performance hit and complexify the code too much. Don't retrieve markers of successor sets which makes obslog filtered output more limited in 4.3.

compat: add a fixed version of mergecopies for hg<=4.3 In hg<=4.3, copies._fullcopytracing() does not exist and we have to wrap copies.mergecopies() to fix the AssertionError coming from core.