Merge branch 'en/t6042-insane-merge-rename-testcases'

Various glitches in the heuristics of merge-recursive strategy have been documented in new tests. * en/t6042-insane-merge-rename-testcases: t6042: add testcase covering long chains of rename conflicts t6042: add testcase covering rename/rename(2to1)/delete/delete conflict t6042: add testcase covering rename/add/delete conflict type