only build matcaffe as part of 'make everything' if MATLAB_DIR is set
don't do runtest as part of 'make everything'
Merge pull request #1658 from jeffdonahue/make-everything-tweaks

'make everything' tweaks
add missing value support to SoftmaxLossLayer
add spatial normalization option to SoftmaxLossLayer

With missing values (and batches of varying spatial dimension),
normalizing each batch across instances can inappropriately give
different instances different weights, so we give the option of simply
normalizing by the batch size instead.
clean up formatting in SoftmaxLossLayer