Docs Makefile additions, compute/numpy tests.

Fixes the problem of capabilities.py failing to create the graph the first time docs are built on a machine. Simple fix. Also, there are some tests and random changes to compute_numpy in here that I added in. Going to remove the other pull request. @mrocklin @cpcloud 
OK, if you don't know how to cover it but still don't want to remove it then we should probably leave it as uncovered.  Maybe someone later will come by and figure it out.   Is suggest removing the pragma here.  Those should be used very sparingly.