Garbled output of cache.inc doxygen

http://api.drupal.org/api/function/cache_set/7

After reading through this, we definitely should open a separate issue to convert this variable system blow-up:

 * To make Drupal use your implementation for a certain cache bin, you have to
 * set a variable with the name of the cache bin as its key and the name of your
 * class as its value. For example, if your implementation of
 * DrupalCacheInterface was called MyCustomCache, the following line would make
 * Drupal use it for the 'cache_page' bin:
 * @code
 *   variable_set('cache_page', 'MyCustomCache');
 * @endcode
 *
 * Additionally, you can register your cache implementation to be used by
 * default for all cache bins by setting the variable 'cache_default_class' to
 * the name of your implementation of the DrupalCacheInterface, e.g.
 * @code
 *   variable_set('cache_default_class', 'MyCustomCache');
 * @endcode

...to the approach that the new MailSystemInterface is using -- one variable that serves as router to cache bin implementation assignments.