test-copies: introduce merge chaing test for the A/E + change tests This is similar to the chaining test we have for the A/E merges (without change). The current result of this tests is wrong, as for they "without change counter part". This will be fixed by a later changesets. Differential Revision: https://phab.mercurial-scm.org/D10052

test-copies: add a "change during merge" variant to the A+E test Checks inline comment for details.