REST: add fnname

I have been failing in getting my python code to work because it was being rejected as invalid. I traced this to a new? requirement that the api function being referenced is indicated by the key 'fnName', which has a value of the form 'civicrm/X/Y' where - I think - X is the entity and Y is the action.

This change adds the new key in, and I can confirm that what previously failed now works.

It is unclear to me whether this change means that 'entity' and 'action' keys are now redundant, though I suspect they are.

Please comment/ask/say why I'm wrong if needed!

Server in question is 4.4.5 running in Drupal 7