Breaking change: use correct language pack path for the plugin

See https://core.trac.wordpress.org/changeset/22346
Allow additional post-type CSS classes to be passed as a second parameter.

Props bbPress revision 4790
In breadcrumb, skip crumb if parent is empty or an error.

Props bbPress revision 4787
phpDoc correction
INTERIM commit adding first bit of integration of BuddyPress.

Not ready for test or production.