New DB_TIMEOUT Constant in wp-config.php to be used in wp-db.php

[sc0ttkclark]

This is really just highlighting a fix that I found useful:

​http://thesocialmediaguide.com.au/2010/07/31/solution-for-wordpress-database-error-mysql-server-has-gone-away-for-query/

I believe by making this a core thing, by just hooking in with DB_TIMEOUT, this can help people tweak their configurations more easily.

Code could be:

if ( define( 'DB_TIMEOUT' ) AND DB_TIMEOUT > 0 )

$this->query("SET SESSION wait_timeout=" . DB_TIMEOUT);

[nacin]

I don't like this as a constant. Regardless, better done in the context of #5932.