People might put more extraneous whitespace in a @since line in a
documentation comment, which should not affect the ordering of
methods/signals/etc. in the generated output.
https://bugzilla.gnome.org/show_bug.cgi?id=770372
Most changes were just replacing usage of "has_key" with "in".
Also updated the sorting function which was simplified and
changed to a "key" function instead of "cmp" (which is no longer
supported in python3. Verified everything builds with
python 2.7 and 3.
https://bugzilla.gnome.org/show_bug.cgi?id=678066