Fix SoftmaxLayerTest: forgot to change this one to use DtypesAndDevices;
was causing Travis build to randomly fail if a previous test had set the
mode to GPU (which no test that is run by 'make runtestnogpu' should, so
I guess there's another bug somewhere).
Merge pull request #698 from jeffdonahue/softmax-layer-test-devices-fix

Fix SoftmaxLayerTest: forgot to change this one to use DtypesAndDevices;
fix choice of clang++ in OS X build
[example] elaborate net surgery description
Fix Makefile warning error message.
use layer_param instead of layers_[layer_id]->layer_param()
Add param_propagate_down_ vector to layer, populate according to
blobs_lr in Net::Init
Make ConvolutionLayer and InnerProductLayer abide by param_propagate_down_
Use Blobs instead of SyncedMemorys for the bias_multiplier_'s.
Add Net Test to verify correct param_propagate_down behavior.
Merge pull request #660 from jeffdonahue/param-propagate-down

Conditionally compute parameter gradients
Another bugfix related to my CPU/GPU test changes: make NetTest a
MultiDeviceTest (Caffe:set_mode(Caffe::CPU/GPU) isn't run without this).