Better error messge if we asked for cudnn but it isn't available.
Make CPU conv2d test use floatX.
small code cleanup
fix error detection.
doc to get error if we can't use cuDNN
pep8
Add theano.tensor.extra_ops.to_one_hot
Speed up DownsampleFactorMaxGrad.perform
doc
Make a test faster
[TEST] fix new test with cuda.
Add installation doc for Ubuntu 14.04
Make verify_grad don't mix float32 and float64
Better error message.

fix gh-2224
Print the optimized scan graph
pep8
In verify_grad, cast the projection to float32.

This help gpuarray tests to run on device that don't support float64.
typo/comments
Fix tests due to change to gradient check dtype.
Fix overflow that cause crash in CudaNdarray_ZEROS