missing c_set_tensor4d in GpuDnnConvBase
Merge pull request #2241 from ynd/dnn_conv_fix

missing c_set_tensor4d in GpuDnnConvBase
Catch exception if open() fails as well.

Drop support for python 2.4.
Merge pull request #2244 from lamblin/fix_setup_readonly

Catch exception if open() fails as well.