Doc

Remove a bad unit test

these were caught by my recent input validation pull request, which was
merged before travis could run on it

theano.gradient setup (it was checking that the internal implementation
of grad worked in a specific way, using None values that are not
even allowed anymore)

Fix tests failing with DebugMode.check_preallocated_output=ALL

Add validation of input for some ops

Fix Switch.grad

The other modes would trigger errors, segmentation faults, or wrong
results, if the next Op was working inplace.

Tan test range

Grad switch

Import

Sparse grad import

Update doc to mention theano-nose instead of nosetests

A c version for softmax almost identical to the bias softmax one