patch: add label for coloring the index extended header
Just like the summary says, this will colorize the:
index 3d3ba4b65e11..57274a0f46b2 100644
line in the diff output.
--- a/mercurial/patch.py Sat Dec 31 15:41:57 2016 -0600
+++ b/mercurial/patch.py Mon Jan 09 10:59:45 2017 -0800
@@ -2343,6 +2343,7 @@
('old', 'diff.extended'),
('new', 'diff.extended'),
('deleted', 'diff.extended'),
+ ('index', 'diff.extended'),
('---', 'diff.file_a'),
('+++', 'diff.file_b')]
textprefixes = [('@', 'diff.hunk'),