tests: make chunk header of external diff glob-ed for portability Before this patch, some tests using external "diff" command via extdiff extension fail on Solaris, because system standard "diff" (= /usr/bin/diff) on Solaris always formats chunk header in the style below: @@ -X.x +Y.y @@ even though "diff" on Linux sometimes omits ".x" and/or ".y" in it. This patch makes chunk header of external diff glob-ed for portability of tests, and adds check-code.py rules to detect such diff output in tests. This patch also changes "hg diff" output in test-subrepo-git to simplify detection rules, even though it is certainly portable because these lines are generated by "git" command. This patch is a part of making tests using external "diff" portable, and tests below aren't yet portable even after this patch. test-largefiles-update.t test-subrepo-deep-nested-change.t