tests/test-backwards-remove.t

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

  $ hg init
  $ echo This is file a1 > a
  $ hg add a
  $ hg commit -m "commit #0"
  $ ls
  a
  $ echo This is file b1 > b
  $ hg add b
  $ hg commit -m "commit #1"
  $ hg co 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved

B should disappear

  $ ls
  a