Replace the ancient `phpfreaks.com` RegEx to extract urls to ping with a more robust matcher. URLs with commas and things like `&amp;` were not being pinged. The new matcher even works for most IDN URLs. Adds unit tests.

Fixes #9064.



git-svn-id: https://develop.svn.wordpress.org/trunk@25313 602fd350-edb4-49c9-b593-d223f7449a82