gcc-changelog: Add warning for auto-added files

gcc-changelog: Add warning for auto-added files

git_email.py prints now a warning for files added automatically.
git_check_commit.py does likewise but only with --verbose.
It prints one line per ChangeLog file, either stating the file
or if more than one the number of files.

contrib/ChangeLog:

	* gcc-changelog/git_check_commit.py (__main__): With -v print a
	warning for the auto-added files.
	* gcc-changelog/git_commit.py (GitCommit.__init__): Add self.warnings.
	(GitCommit.check_mentioned_files): Add warning for auto-added files.
	(GitCommit.print_warnings): New function.
	* gcc-changelog/git_email.py (__main__): Remove bogus argument to
	GitEmail constructor; print auto-added-files warning.
	* gcc-changelog/test_email.py (test_auto_add_file_1,
	test_auto_add_file_2): New tests.
	* gcc-changelog/test_patches.txt: Add two test cases.