Improve mex all error handling.
Improve mex all error handling.

pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/shared-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff,pdbartlett/misc-stuff