__ref__,__deref__ handling

[KrisThielemans]

https://github.com/jaeandersson/swig/blob/cd3f6c5fe9ed273fcc981dcae3e8b50d51529664/Lib/swig.swg#L426-L428 needs to be changed for MATLAB, as it doesn't allow functions starting with _. This creates an error in the test-suite

ERROR: Error: File: /home/kthielem/devel/build/swig/Examples/test-suite/matlab/+smart_pointer_member/Bar.m Line: 17 Column: 26
Invalid text character. Check for unsupported symbol, invisible character, or pasting of non-ASCII characters.
   smart_pointer_member failed

That seems trivial, but then the question is what to do with them... Octave has https://github.com/jaeandersson/swig/blob/cd3f6c5fe9ed273fcc981dcae3e8b50d51529664/Lib/octave/octtypemaps.swg#L80-L90 which might be related? Maybe not as this is stuff with SMARTPOINTER, which we currently don't have in the Matlab module.