move using statements inside namespace caffe to avoid polluting the whole name space.
neuron_layers.hpp should not need to include leveldb
configure Makefile for CPU-only build
stub out GPU layer methods to crash loudly in CPU-only mode
add guards to drop GPU code in CPU-only mode
collect CUDA includes and calls, separate from CPU-only mode, leave out

- collect CUDA includes in device_alternate.hpp
- add guards for CUDA code
- move GPU code into cu from cpp
- make CUDA includes and libraries conditional in Makefile
- drop CUDA dependency from travis-ci build
switch travis build to CPU-only flag, drop runtestnogpu target
relax benchmark test timing for cheap hardware / CI build
check CPU-only everything, CPU + GPU build with travis
Merge pull request #561 from shelhamer/cpu-only-build

CPU-only build

no GPU, no CUDA, no problem!
compute_image_mean namespace fix.
Merge pull request #716 from Yangqing/dev

Minor Code Cleaning
More namespace cleaning.
remove 2 using per jeff's comment
fixing std::min and std::max and std::abs: using them in default will make nvcc unhappy.
Merge branch 'dev' of https://github.com/BVLC/caffe into dev

Conflicts:
	src/caffe/common.cpp
lint
Merge pull request #718 from Yangqing/dev

More namespace cleaning.
Merge branch 'dev' of https://github.com/BVLC/caffe into dev

Conflicts:
	include/caffe/common.hpp
	src/caffe/layers/window_data_layer.cpp
	src/caffe/solver.cpp
	src/caffe/util/io.cpp