Hocr filename fix

This is Paul Pound's HOCR filename fix that got pulled into head yesterday,  Basically, the latest version of Tesseract has changed its hard-coded extension for HOCR files from HTML to HOCR.  For the Group demo I hacked things to accept HOCR and added it to /etc/mime.types as text/html, but this works too, and since it's now in HEAD....

Not sure quite what happened with a couple of the tabs.  Sorry about that.