Add new do_action before forum topics loop on Forums directory

[r-a-y]

Would be nice to see a new do_action before the forum topics loop begins on the Forums directory page.

This is to allow theme designers to hook additional content right after the [h3].

On line 68 of /bp-themes/forums/index.php, change:

<form action="" method="post" id="forums-directory-form" class="dir-form">

to:

<?php do_action( 'bp_before_directory_forums_topic_loop' ) ?>

<form action="" method="post" id="forums-directory-form" class="dir-form">

Name the do_action whatever you want!

[r-a-y]

Was inspired by this thread:
http://buddypress.org/forums/topic/bp-forums-forum-index-instead-of-latest-discussion

[boonebgorges]

(In [3401]) Adds do_action hooks before and after the forums directory form. Fixes #2139. Props r-a-y