Load plugin template files without requiring extra installation step

[DJPaul]

Any non-basic plugin will introduce new pages for its component into a BP site. This requires end-users to move the template files out of the folder. This sucks because after the one-click plugin install introduced in WP 2.7, you still have to log into your server to finish installing the plugin.

The proposed patch will call an action when it tries to load a template file which doesn't exist in the currently active site theme. This will allow BuddyPress plugins to hook in to the chain of events and remove the extra installation step that otherwise has to happen.

If a user does choose to move the plugin template files into their site theme, those will be loaded instead allowing them to be easily customised if so desired.

[DJPaul]

Second patch is less rubbish.

[DJPaul]

ticket_954-3.patch works. A plugin author would implement the action as per this example which I use in my Achievements plugin: ​http://buddypress.pastebin.com/f1c094f38

[DJPaul]

To put the pastebin snippet above into context, I am loading the screen file with the following (as usual):

bp_core_load_template( 'achievements-member-theme/summary' );

[apeatling]

(In [1930]) Fixes #954