One tests is failing: theano.sandbox.gpuarray.tests.test_blas.py:GpuGemvTester.test_all due to this opt.

The class Gemv and CGemv make_node don't need that all inputs have the same dtype, but the op GpuGemv have this restriction. I see 2 fixes, make this op support other dtype for scalar as the cpu op, or check for that before doing the opt. I think it would be better to support the same thing as on the CPU.

Can you do that? Do you prefer to fix this in another PR or in this one?