Preprocess bug causes forums to not show up

This is a weird one, and I'm hard-pressed to reproduce it, but regardless of cause and effect, the attached patch should be committed anyways, to make the generated $prefixes array structure similar to that returned by module_list().

In d6_compat.inc, you define the default preprocess function, $prefixes[] = 'template';, which will eventually map to template_preprocess_forum() (same file). However, because you define it without an array index, it gets stored as: [0] => 'template'. You then add all the modules to the list via module_list(). That function sets modules as ['block'] => ['block']. At the very least, the attached patch will set 'template' to be list the rest of the modules.

However, I think there's also a bug here that recently bit my site (where we ended up truncating the cache, which called a recreation of this preprocess function list). After adding 'template' and all the modules to the $prefixes, you run through a blacklist routine to remove 'search' from the lookup. You end up doing this great foreach with an array_search and all this crap (when you could simply do unset($prefixes['search']), which would also be another legitimate fix/patch). When search.module isn't enabled (and thus, not returned in module_list), array_search() will return FALSE. The code, however, blindly will attempt to unset [$prefixes[FALSE]], which I BELIEVE kills off [0] => 'template'. Removing 'template' from the prefixes list breaks the entire module (since template_preprocess_forums is never run).

Ahem.

Nutshell? Apply this patch ;)