Also add ".prod()" method to tensor variables.

This enables specifying the dtype in which the internal summation
should be done, like in Numpy.

Also add a tests for one specific case.
The usual cases should be tested by the regular tests, since the sum
nodes' dtype are no longer allowed to be None.

Update existing test to check that a TypeError is raised if an
inappropriate output dtype is specified in sum().

It's easier to understand the doc if we have explicit kw args.

If the output dtype would force a downcasting of the values
(for instance, summing a float vector into an integer), a TypeError
is now raised.

Also, a Sum node has to have a non-None dtype. It is checked in
make_node because for some reason the pretty-printing mechanism needs to
instanciate "Sum()".

PEP8 and docstring fixes.

Fix test in TrueDivTester

Since dtype mismatch is one reason the error is raised, it makes
interpreting it easier.

Fix Ger C code when output is a row or column.

Some BLAS versions did not accept (1,1) strides in that case.

Update tests, gpu_gemv is used now, not gemm/dot22

Fix test of elemwise_fusion, now intdiv is fused.

more helpful error to catch symbolic shape vecs in infer_shape

Add warning for bug in Numpy <= 1.6.1.

When using numpy's advanced indexing on huge arrays (2**32 elements or
more), Numpy <= 1.6.1 has a bug where the resulting array is not
properly filled. We emit a warning in those cases.

Use C code for Alloc of broadcasted scalar

Fix blas tests

C code for integer division

Minor stuff

Thanks Olivier :) Is great to have someone like you involved in the project, that is able to notice and fix all the small details.