Fix to verify_grad if the output of the grad is sparse, but not the input.
Better error message.
Add ConstructSparseFromList tests.
Add theano.sparse_grad interface.
New internal interface to the sparse grad of AdvancedSubtensor1
Better doc of theano.sparse_grad
update comment following code review.
Added comment.
Merge pull request #1448 from nouiz/adv_sub1_grad

Add theano.sparse_grad interface.