test-run-tests: glob away a --debug run difference on Windows

This internal test is piped through 'grep -v pwd' to eliminate the pwd alias set
when running with MSYS.  Unfortunately, the '.' from the successful run of the
prior internal test precedes the pwd alias for the next test on the same line,
so grep filters out '.' too, except for the final test.

It also looks like there may be a bug with --debug: the output of the internal
test that had this diff says 2 ran, 0 failed (one test being test-failure.t),
but if --debug is omitted from the internal test, then it says 2 ran, 1 failed.

With this longstanding issue fixed, the test suite finally runs cleanly on
Windows (except subrepo merge documented in issue 4988), with 88 skips.  \o/

tests/test-run-tests.t

@@ -238,7 +238,7 b' Running In Debug Mode'
   babar
   + echo *SALT* 4 0 (glob)
   *SALT* 4 0 (glob)
-  .+ echo *SALT* 0 0 (glob)
+  *+ echo *SALT* 0 0 (glob)
   *SALT* 0 0 (glob)
   + echo babar
   babar