ignore the new html docs stamp files
fix gitignore to ignore generated docs

The "**" syntax was introduced sometime between git 1.7.9.5 (which is
in Precise) and 1.8.5.3, but luckily for this pattern we don't need it.

This commit makes generated docs be ignored on Precise and earlier,
while not breaking things (hopefully) on newer versions of git.
Merge remote-tracking branch 'origin/v2.5_branch'

Conflicts:
	src/.gitignore (switch to anchored patterns to match the
            surrounding syntax)