Blogs: Use a more specific selector to disable subnav AJAX clicking.

When on a user's blogs page, BuddyPress unintentionally hijacks clicks to
subnav tabs with AJAX.  BP Follow attempted to remove this hijacking, but
on some themes, the older .item-list-tabs selector wasn't specific enough.

This commit uses "#subnav a" as the selector and should fix the majority
of themes.

See #31.