Exposed baseHref to catandtag.tpl

This allows some google crawl errors to be fixed by supplying a full path to resources.
Changed relative links to full paths.

This fix uses the FAQ variable `baseHref` resolve some Google crawl errors.
Changed social networking links to nofollow.

It seems the `.pdf` documents for the FAQ are given precedence over the actual web page.
This uses `nofollow` to solve the problem by preventing page rank from flowing to the social network & `.pdf` buttons.
Added C++ and Plain brushes to syntax highlighter.
Added fix for abbr tags in code.

The PHpMyFAQ system currently adds glossary entries into `<code>` tags.
As they are embedded within `<pre>` tags, the `<abbr>` tags are not rendered as html,
but as plain text inside other code.
Merge pull request #885 from Chris--A/patch-1

A small patch fixing a a few bugs, missing elements.
Fixed RSS/Atom feed compatibility, closes #886
Improved category selection usability
Fixed sent mail to category owner, closes #891
Updated release date
Prepare release
Added missing shebang
2.8.12 -> 2.8.13
Merge branch '2.8' into 2.9