Fix hard crash when dividing by 0

fix opt warning in the ifelse lifter

Updated numpy as np #4218

- use KERNEL macro
- do not use `%(fail)s` on GPU to avoid returning prematurely from
  kernel
- have special block for y == 0 (and reorder other ones)
- keep calling // 0 or % 0 on GPU, even though cuda will not fail

Disable compute_test_value during Theano optimization phase. This giv…

Setting gradient for MRG_RandomStreams distribution variables to be null

Update Windows (and other generic) installation instructions

Gpu cholesky

initial commit for gradient for MRG_RandomStreams distribution variables should be null - issue #4078

and list of requirements.

Always import gpuarray.rng_mrg to have its optimizer imported.

Use Op params for GpuDnnSoftmax

move buildbot cache outside workspace

Better error message when an opt make an invalide replace.

Even if the output shape is incorrect, we should not crash.