'bp_head' hook does not exist for theme compat

[r-a-y]

bp-default has a hardcoded do_action( 'bp_head' ) in its header.php.

bp-legacy does not have such a hook. So any code hooked to 'bp_head' will not run when a theme other than bp-default is activated.

In r6529, I added the 'bp_head' hook to 'wp_head', but quickly reverted it due to backwards compatibility as explained in r6177.

In 01.patch, I've added the 'bp_head' hook to the BP_Theme_Compat class. This is so any classes that extend it like BP_Legacy and BP_TurtleShell can inherit it.

[r-a-y]

Disregard this patch. BP_Theme_Compat class needs to be refactored entirely. New ticket will be created for this.

[johnjamesjacoby]

(In [6605]) When in theme-compat, make sure 'bp_head' gets added to 'wp_head' action. Also introduce bp_head() function, and use in bp-default header.php. Fixes #4669.