[WIP] SciDB backend

This isn't ready to merge, but I've started playing around with connecting SciDB to blaze.

There are two failing tests currently (I think one is a backend bug, and one is a SciDB bug). I also want to add some more tests to make sure I understand how blaze is working.
I don't expect to merge #688 in the near future.  Lets cross that bridge when we get to it.  I'm also happy to provide a patch with the necessary renamings.