Dear Maintainer,

Ikiwiki documentation states, that 'highlight' plugin does
directive/wikilink expansion, when highlighting entire files, but does
not state, that it does this, when used in 'format' directive. Still, it
does this, and confuses 'format' (or vice-versa, but since this
functionality is documented in 'highlight' plugin, I expect it to be its
fault).

Example:
-------------------------------------------------------------------------
tsubasa:~/tmp/iki$ cat a/b.mdwn
[[!format sh """

if [[ foo ]]; then
bar

"""]]

tsubasa:~/tmp/iki$ ikiwiki --plugin format --plugin highlight a b --rebuild
tsubasa:~/tmp/iki$ grep if b/b/index.html
53:<pre class="hl"><span class="hl kwa">if</span> <span class="hl opt"><span class="createlink">span> foo <span class="hl opt"></span>;</span> <span class="hl kwa">then</span>
-------------------------------------------------------------------------

As you can see, something strange happens on [[ ]]. It does something
similar, if I use [[!map ]] directive there - listing is embedded, but
again, corrupted.

Version in unstable (20121017) also have this bug.

It would also be a good thing to have this feature (directive/link
expansion) optional - either as global option, or as argument to
directive.