tests: save the original PATH and PYTHONPATH variables When running the tests, define ORIG_PATH and ORIG_PYTHONPATH environment variables that contain the original contents of PATH and PYTHONPATH, before they were modified by run-tests.py This will make it possible for tests to refer to the original contents of these variables if necessary. In particular, this is necessary for invoking the correct version of hg for examining the local repository (the mercurial repository itself, not the temporary test repositories). Various tests examine the local repository to check the file lists and contents of commit messages.