Remove TABs from src

Will also make selftest to check that they aren't introduced

Removed trailing whitespace from all .sml and .sig files.

This affects over 900 files and was done using emacs's delete-trailing-whitespace
function in batch mode. Building the system with Poly/ML and Moscow ML seems to
work, so I'm hoping these changes don't break anything. Please complain if
they do!

Incorporating utilsLib into mutrec, since that's the only place it's used
(and it's kind of basic to be considered a full-fledged library).