merge: respect parents order when using `graft` on a merge The previous code did not record the index of the replaced parent. It was always using the "graft" destination as `p1`. This could switch parents order in some situation (eg: some of the evolve evolving merge case). Recording and using the information fixes the issue in evolve. We are not aware of core commands calling graft in that fashion, so we could not build a simple test case for it using core commands.

tests: register test-merge-combination.t as small but slow run-tests.py use file size as an heuristic for test run time. The new `test-merge-combination.t` is a small file that do a lot of processing. As a result it tend to be scheduled really late but delay the full test run by a lot. On an example test run, the one-before-last test completed 279s after the start of the run, while `test-merge-combination.t` finished 355s after it. A 76s delay. This delay can be avoided since `test-merge-combination.t` only got started 175s after the start of the run.

test: allow different result for zstd compression (issue6188) test-repo-compengines fails on big-endian due to different file size, but the repo doesn't seem broken, so allow both sizes. Differential Revision: https://phab.mercurial-scm.org/D6787

Added signature for changeset a4e32fd539ab

Added tag 5.1.1 for changeset a4e32fd539ab

python-zstandard: apply big-endian fix (issue6188) This is a port of commit d4baf1f95b811f40773f5df0d8780fb2111ba6f5 from the upstream project to fix python-zstandard on 64-bit big-endian.