merge: move constant assignments a bit and use them more

merge: change priority / ordering of merge actions The ordering of actions matters. Normal file system semantics is that files have to be removed before a directory with the same name can be created. Before the first ordering key was to have 'r' and 'f' actions come first, secondary key was the filename. Because of future refactorings we want to consistently have all action types (with a sensible priority) as separate first keys. Grouped by action type, we sort by filename. Not processing in strict filename order could give worse performance, especially on spinning disks. That is however primarily an issue in the cases where "all" actions are of the same kind and will be grouped together anyway.

run-tests: fix --interactive option ``TTest._testpath`` never existed. This must be the remain of some contributors side refactoring.

run-test: fix AttributeError in the --interactive prompt One must choose between ``"y yes".split()`` and ``('y', 'yes')``. I choose the later. The feature still crash when you answer "yes" to use it. But at least, the prompt itself works.

run-test: restore the -i prompt by write .err before checking if it exists The `--interactive` flag workis by overwriting the original test file by its `.err` version. So we need to write it before calling `self.fail`. Otherwise the `.err` file does not exists and `--interactive` is ignored. We can move that block code around because it is dedicated to write changed output and we moves it in the try-except dedicated to handling changed output. Note that the flog is still badly broken after this change. But at least it crash instead of being ignored.

run-tests: move _gethgpath() into TestRunner

run-tests: move string escaping to TTest With this patch, TTest is almost fully self-contained and extractable. Only logging functions remain outside of its class.

run-tests: add some docstrings

run-tests: move createhgrc into Test

run-tests: move SKIPPED_PREFIX and FAILED_PREFIX into TTest