tests: use pyflakes module instead of pyflakes executable This results in that the pyflakes version specific to the configured Python version is used. This way, both the Python 2-specific and the Python 3-specific pyflakes are run by the test suite (depending on the configured Python version). For downstream projects which are using Mercurial’s test infrastructure and are not yet ported to Python 3 (e.g. hg-git) it ensures that the correct pyflakes version is run even when the system’s default pyflakes is the Python 3-specific one.

copies-tests: add a case where with merge with an overwritten files This is similar to the BF/FB case, but in this case, the other branch updated the file. So an actual merge happens and the two "independant" file history has to be merged. Differential Revision: https://phab.mercurial-scm.org/D8242

copies-tests: add a case where a file is deleted/added but with a merge This is a case similar to DB/BD, but in this case the other branch updated the file. So an actual merge happens and the two "independant" file history has to be merged. Differential Revision: https://phab.mercurial-scm.org/D8241

copies-tests: add a test with a rename overwriting another file This is a variation of the "BD" case, but this time, the file is not "new", it is overwritten by another file being renamed. Differential Revision: https://phab.mercurial-scm.org/D8240