Defenition cache not loaded

When implementing htmlpurifier as a module on a multisite environment I encountered errors that the required library folder wasn't writable. Our security policies restrict writing in other environments than your own site for obvious reasons.

While debuging the code I found out that the packaged drupal defenition class wasn't used and the default serializer was used instead. Conform to the htmlpurifier documentation I set the "Cache.DefinitionImpl" configuration directive to "Drupal" inside the _htmlpurifier_get_config function.

This seems to have fixed the problem for me. Hope it helps.