fix some clang 3.3 warnings

for this purpose, put the print* and write* debugging functions into
the namespace Opm::Debug and swap out their code to a new
"AutDiffHelpers.cpp" file.

Also, some private attributes were unused. this patch only comments
them out to have them back quickly if necessary...

Finally, some standard headers were included inside the Opm
namespace. This seems like a mishap...

Thanks to @bska for the review!