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.

added 3 theano flags optimizer_including, optimizer_excluding, optimizer_requiring. If using the default mode, this allow to select via the corresponding fct the optimizer to use.

fix bug in optimizer sequence that make the op CrossentropySoftmaxArgmax1HotWithBias and GpuCrossentropySoftmaxArgmax1HotWithBias not being inserted used on the gpu. This caused stability and slowness on the gpu.

CudaNdarray.__setitem now accept an ndarray as a value. It copy the data direction. Restriction, no broadcasting, the CudaNdarray slice must be c contiguous.

optimized memory usage on the gpu: when used gpu_shared_var.value = ndarray, we keep only one memory region on the gpu.

attrs is unhashable since its a list. Fix is to first convert attrs to string
than hash the string.

make the GpuElemwise return the same error as Elemwise when the shape mismatch. Modif test for this.