Compile a binary to run all tests at once.

Addresses #174.

This pull requests adds a new make target for a `test_all.testbin`. Running this binary will run all tests. This is preferable to the current for-loop method of running each binary individually, since it will report a single summary once all tests complete.

This required a few minor changes to the test_caffe_main header.

I am by no means a Makefile expert, so I am very much open to comments on my Makefile edits.