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

Update installation instructions for Windows

fix gh-915. But this don't fix the theano-nose import problem when outside the Theano dir.