Fix typo in debug set text.
Rewrite split() function.  Previous version occasionally lost data.  New version
is simpler.
Fix: Calling print_set with a null set parameter generated a runtime error.
Adjust error message to include title, if it was passed in.
Merge pull request #588 from Kinematics/4.1

4.1
Merge pull request #589 from Windower/4.1

Merge update