[Trac] Escaping underscores

[Emmanuel Blot]

> Any thoughts from others as to removing underlining ability in Trac or
> to making the prefix characters installation configurable?

I think the verbatim mode used by ReStructuredText is better than the
heavy Trac syntax - ` ` vs. {{{ }}}.

I don't use underline in Trac anyway. As already reported, underline
is too much confusing with links from my point of view.