allow cxx flag to be full path to compiler
pep8
add docstring and swap parameter order to be the same as make_node
doc cudnn stuff
Now by default, if cuDNN is available, always use it.
better doc
make dnn detect if the library can be loaded.
Better error message when Theano isn't able to use cuDNN
change error type
fix to use user specified compiler
Always use the tag cudnn
Detect if we are able to init cuDNN handle before auto enable it.
Merge pull request #2239 from nouiz/dnn

Dnn default and doc
check specified compiler is g++
Merge branch 'master' into allow_cxx_flag_full_path

Conflicts:
	theano/gof/cmodule.py
fix error message
improve waring message
Merge pull request #2242 from cocu/allow_cxx_flag_full_path

allow cxx flag to be full path to compiler
Implemented grad for cudnn softmax.
Incorporated reviewer comments.