trying to send webmentions hangs with a 500

I put in http://arstechnica.com/information-technology/2015/11/googles-amp-an-internet-giant-tackles-the-old-myth-of-the-web-is-too-slow/ to send webmentions to the indieweb posts linked, and it took a while then showed a 500

No file or test is named. Start by reproducing the webmention send with the linked Ars Technica URL and capture where the request hangs or returns 500. Done means the linked posts can be processed without a timeout or server error.

Written by the indexing model from the issue text.