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.


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git-svn-id: http://core.svn.wordpress.org/trunk@25275 1a063a9b-81f0-0310-95a4-ce76da25c4cd