fix bug in conv op on the gpu that make the code crash in some case. We don't generate bad result, but read memory that was not usefull and outside the image range.

add new version of Windows documentation that use pythonxy to have a simpler installation. Their is test instruction for the gpu on windows.

make GpuFromHost return a dtype of the same dtype as the input. As CudaNdarray support only float32, an error will be raised.

fix MakeVector.make_node to upcast its input correctly. fix stack to don't downcast float* to int64 and to don't upcast inputs more then necessary.

MakeVector.make_node upcast the input to the dtype received in __init__, but don't allow to loose precission.

fix a bug in optimization of two consecutive sum. Add a warning when we hit this case. The warning can be disabled by the theano flags warn.sum_sum_bug=False.