Bugs fixed in the euclidean loss layer.
Forgot to add the definition for caffe_gpu_sub()
Changed loss function to 1/2 ||x-y||^2 and updated the test cases to test the same.
Changed testing macros to EXPECT_NEAR.
Merge branch 'euclideanlossbugfix' of https://github.com/aravindhm/caffe into unsupervised

Conflicts:
	include/caffe/util/math_functions.hpp
	include/caffe/vision_layers.hpp
	src/caffe/layers/loss_layer.cu
	src/caffe/test/test_euclidean_loss_layer.cpp
	src/caffe/util/math_functions.cu