fixed image_path reference broken in ef1e4d6f34da4c0f7031b144757cdc99396...

...431d7

Looks like $base_url was getting cleaned up but $image_path was broken when the point where it was defined was commented out.  There may be a cleaner approach that that commit was going for, but I just added the $image_path = drupal_get_path('module', 'islandora'); back.

This resolves the error message we were getting that $image_path isn't defined.