Introduces bp_before_directory_members_tabs action hook

This action provides a place for plugins and themes to insert content after
the member directory search box is rendered.

Fixes #4934

Props dontdream

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7118 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Pass $user_nicename to bp_core_get_userid_from_nicename filter

Fixes #4975

Props megainfo

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7119 cdf35c40-ae34-48e0-9cc9-0c9da1808c22