fix Makefile comment about library names
Add --keep-going flag to first make so that any targets that can be
built are built; write out full -j flag as --jobs for clarity.
Run Travis build on all branches (remove whitelist from .travis.yml).
Replace CUSTOM_CXX env var to specify non-default C++ compiler.
Add blank lines between fields for readability.
Merge pull request #694 from jeffdonahue/travis-tweaks

Travis tweaks -- make --keep-going; build on all branches; replace CUSTOM_CXX <eom>
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.