Speed up the gradient of AdvancedSubtensor1 WIP

Add information to error message.

Fix infinite opt loop

Lazy import of sparse module and rename sparsegrad according to python coding style.

Even in DebugMode, even before the inplace phase.

It helps locating infinite loops

Add a flag to decide which gradient should be returned from AdvSubtensor1

Tensor Type has now a sparse grad attribute which can be set or unset to determine if sparse gradient is to be enabled or not. Note if needed, we can provide getters and setters to set the attributes to provide more clean interfaces to application. Right now application can access this attribute and set it before calculating gradient

Ready for merge: Streamline dot & tensordot / Allow dot products of n-dimensional variables

Fix bugs reported by the DL tutorial wrote by Nicolas

Fixed a race condition.

Importing Scipy sparse in the ContructSparse Op to avoid unnecessary Scipy dependency.

Fix crash tensor.roll(Var, iscalar) reported by Jeremiah Lowin.

fix gh-1154

Issue #1164: Fixed failing test_pycuda_example.

Removed unnecessary #includes from generated cuda code.

Denormal