Fix for potential crash due to concurrent jobs

Installation instructions, and test fixes, for windows

I corrected what I thought was a typo in a previous pep8 commit,
but this change was also needed for the test to make sense.

That is basically what numpy does, and it is necessary under win64,
since all shapes are composed of long, not int.

Pep8

Crash size 0

Yet another size fix

Minor stuff

enable_sparse is indeed a Boolean

Fix composite new inputs

It happen in a particular execution order of this optimization and the
element-wise fusion optimization when upcasting some inputs to
float32 (to compute them on the gpu).
(Frederic B., reported by Sander Dieleman)

Fix for win64

New interface for scan

Gpuconv