tests: add -R switch Restarts at first .err file if one exists, otherwise runs all tests

tests: sort test list if running all tests

Fix accessing a repository via -R/--repository through a symlink. Sometimes the repository root was compared to os.getcwd(), which always uses the canonical path without symbolic links in it. This would changes self.root of the localrepo objects to always use os.sep as the directory separator, which is implicitly assumed in some places, but may not be the case if somebody uses -R foo/repo on windows.

Merge with upstream