tigefa4u projects Trac

The RSS feeds produced by the TracTimeline, the TracQuery, the TracReport
and the TracRevisionLog should now work as expected.

The following changes have been implemented:
* The item's <title> element should never contain HTML markup,
and only numerical or predefined XML entities are allowed.
* The item's <description> element contains ''escaped'' HTML markup
* Also, the TracRevisionLog RSS feed's <author> elements are not
emitted if there's no author (i.e. no e-mail address for the author)

Closes #2580.