crm_core_activity_ui_add_activity(): type-o and redirect

I've created a patch which makes one type-o fix and adds a feature to crm_core_activity_ui_add_activity() which generates the general "Add an activity" page:

• The title was set to "Add a activity" ('a' instead of 'an') in contrast to the 'title' set in hook_menu(). The fact that MENU_LOCAL_ACTION's don't get their 'title' used is actually a core bug. To work around it, my patch looks up the title used by hook_menu(), so that you don't have to repeat it twice (adhering to the DRY principle - and allowing other modules to use hook_menu_alter() to change the title).
• When there is only one activity type, it will immediately forward the user to the page to add that type. This is exactly the same as the 'node' module does in it's node_add_page() callback, when there is only one node type.

I'll attach the patch in a moment!