Forums use wpdb::wpdb() constructor, which has been dropped in WP 3.2

[boonebgorges]

BP forums extend WPDB to use the shared DB info. This is done using the old PHP4 style constructor for the wpdb class, which is dropped in WP 3.2. ​http://buddypress.trac.wordpress.org/browser/tags/1.2.8/bp-forums/bp-forums-bbpress.php#L144 This means that the forums crash BP installs on the 1.2 branch/WP 3.2

The solution is to use wpdb::construct() instead. Checking in a fix in a moment.

(NB this is already done on trunk, in r4211)

[boonebgorges]

(In [4547]) Use PHP5 constructor when extending WPDB to maintain compatibility with WP 3.2 and BP forums. Fixes #3293