Fix fontification performance bug

Merci vielmal for orglink! Universal Org links have been on my todo list for months.

This patch fixes a curious performance issue.

On my Emacs 24.3.1 system, the following benchmark shows a massive performance drop
when loading a huge C++ file. Unpatched orglink: 0.9 sec vs. patched: 0.04 sec.

    git clone git://github.com/nonsequitur/show-performance-bug.git
    HOME=show-performance-bug emacs --no-splash

I wonder what causes this. It can't be the fontification running twice.