Tensor op, cache

3D separable convolutions

Fix test in the daily buildbot and make sure to don't loose the current linker.

Attempt to lock PR tests to the specific version of libgpuarray that they require.

Add covariance matrix function theano.tensor.cov

Add some tests, to check at least if everything runs well.

Standardize all three files (dnn_fwd, dnn_gi),
to have same code logic and organization across these three codes.

Add fallback entries as fallback functions.

Add `-t` to hash for timed algorithms.