get_action should raise an exception if the action requested doesn't exist

[icmurray]

Original bug report:

Hi CKAN devs,

Can I request that ckan.logic.get_action raises an exception if the action requested doesn't exist?

Two of us had a frustrating time tracking down an exception this morning. It's difficult when the exception is raised in python in a template because you don't get a line number. The problem was caused by a new logic function being added to another extension, and we hadn't updated the code there. So if get_action raised an proper exception rather than silently returning None then I think we'd have found the problem quicker.

I'd write the code for this, but as I understand that the new system would require a ticket, branch, pull request, code review, merge. It seems a lot to do for such a small thing.

Dave