Prevent gpu initialization when not required

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.