Add preliminary support for yosemite

Some changes to the makefile were needed to get caffe built on yosemite.

One change pulled from (https://groups.google.com/d/msg/caffe-users/rXjBlzWkA8c/kEKGeiqZhBAJ)

Build completes and all tests pass, but it's probably good to hold off on merging until someone else with a yosemite dev environment bootstrapped can test it.