Use module_load_include() instead of require/include to avoid facetapi registry problems

Hi,

I got the following error when moving this module to a subfolder in sites/all/modules, even after using Registry Rebuild. It might be preferable to use module_load_include() instead of require_once or include statements, as described here.

[17-Sep-2013 16:46:46 UTC] PHP Fatal error:  require_once() [<a href='function.require'>function.require</a>]: Failed opening required '/path/to/drupal/sites/all/modules/facetapi/facetapi.block.inc' (include_path='.:/Applications/MAMP/bin/php/php5.3.14/lib/php') in /path/to/drupal/sites/all/modules/facetapi/facetapi.module on line 69