Seed rng in tests.
Remove useless debugmode warning about optimization that change results

The error is due to rounding difference. The test that fail randomly is theano/sandbox/cuda/tests/test_conv_cuda_ndarray.py:TestConv2DGPU.test_logical_shapes.

Normally, we should set atol depending of the input shape, but the current structure don't allow this, so I use the output shape. So this could happen with other tests if the output shape is smaller.
Merge pull request #1643 from nouiz/tests

Make a tests more robust to different seed
Make get_scalar_constant_value() support Shape_i()(Constant)
pep8
fix gh-1122 It is a crash fix reported by abalkin
Fix tests crash in DebugMode recently introduced.

Now we keep the original error message type and just add more information to it.
Merge pull request #1645 from nouiz/debugmode

Fix tests crash in DebugMode recently introduced.
Merge pull request #1644 from nouiz/gh-1122

Gh 1122