gcc-changelog/git_email.py: Support older unidiff.PatchSet

gcc-changelog/git_email.py: Support older unidiff.PatchSet

Commit "unidiff: use newline='\n' argument",
r13-4603-gb045179973161115c7ea029b2788f5156fc55cda, added support CR
on a line, but that broke support for older unidiff.PatchSet.

This patch uses a fallback for git_email.py (drop argument) if not
available (TypeError exception) but keeps using it in test_email.py
unconditionally.

contrib/ChangeLog:

	* gcc-changelog/git_email.py (GitEmail:__init__): Support older
	unidiff.PatchSet that do not have a newline= argument
	of from_filename.