.travis.yml and .gitignore: various minor cleanup
Use all caps for global preprocess vars (e.g. EXAMPLES_SOURCE_DIR)
restore .testbin extension, and move caffe_tool back to "caffe".
(Required as I had to change the tool target names to '.bin' but give
them an OUTPUT_NAME, but the .bin made the test_net tool collide with
the test_net unit test.)