test-copies: add 3 new files with their own content The new `p`, `q` and `r` file mirror the `a`, `b` and `h` but with different content for each files. This will be used to create "mirror" test case that involve actual merge happening. For now, we only add the file to keep patches small and easier to review. Differential Revision: https://phab.mercurial-scm.org/D10053

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.