aux scanner for wordpress 3.5 sites with X-Pingback

Just a scanner to work with the other pull request for the wordpress_pingback_portscanner (https://github.com/rapid7/metasploit-framework/pull/1235/).

Attempts to resolve the wordpress feed via feed=rss2 variable and if found reads through the blog posts to attempt to find one that has pingback enabled. Stores findings in vuln database.