Bring the local (previously magento) cache backend up to speed

These commits mostly contain the changes I needed to make in order to get the local storage backend working.  
There is one new feature I needed to add to get it working on a site with a third party ajax shopping cart extension. I added a configuration option to disable caching for ajax requests not originating from Cm_Diehard.  
I think its functional now, even though I'll continue to implement this in a project and probably will send an additional PR in future.  Originally I thought I'd wait with a PR until I was finished, but since you seem to be picking up development again I though it might be good to send it now to avoid duplicate work.