tests: add more tests of copy tracing with removed and re-added files We had a test where the destination of a copy was removed and then added back. This patch adds similar cases where the break in history instead happens to the source file. There are three versions of this: 1. The break happens before the rename. 2. The break happens on a branch parallel to the rename (where copy tracing is done via the merge base) 3. The source is added on each side of the merge base. The break in history is thus in the form of a deletion when going backwards to the merge base and the re-add happens on the other branch. I've also added calls to `hg graft` in these cases to show the breakage in issue 6163. Another factor in these cases is matching nodeid (checked in copies._tracefile()). I've made two copies each of the cases to show the impact of that. One of these is the same as a test in test-rename-merge1.t, so I also deleted that test from there. Some of these tests currently fail, where "fail" is based on my current thinking of how things should work. I had initially thought that we should be more strict about not tracing copies across commits where the file did not exist, but issue 6163 made me reconsider. The only test case here that behaved differently in 4.9 is the exact case reported in issue 6163. Differential Revision: https://phab.mercurial-scm.org/D6599