Send User-Agent when confirming pingbacks with WordPress

Following discussions at the WordPress support forums, bug #1713, the bug was fixed by Changset #2933 In simple English, WordPress confirms pingbacks with a blank user-agent. The latest version of Bad Behavior blocks sites with send a blank user agent, as this is a common technique being used by spammers to get through user agent filters. I faced a similar problem with Silktide and added their IP to the whitelist.