magit/magit — pull request #1446 by tarsius (2014-08-01 00:32:22+00:00)
Title: Massive speedup, thanks to not using looking-back

magit-insert-child-count: massive speed-up

Previously we used `looking-back` to check whether a section's heading
ended with ":" indicating that a child count should be inserted. That
had a devastating effect on performance. We now use `char-before`.
And generally avoid all unnecessary work.