Configurable date regular expression

I'm porting a blog from Tumblr to DocPad and I'd like to preserve existing URLs of the form `post/41935904836/<slug>` generated from documents named `YYYY-MM-DD-<slug>.html.md`.  These documents  have  a custom URL in the YAML head matter.  Trouble is, datefromfilename thinks 41935904 from the URL is the date, not YYYY-MM-DD from the filename, so I end up with documents at `post/836/YYYY-MM-DD-<slug>`.  Yuck.  Customizing the `dateRegExp` to be stricter for my site was the smallest fix.