in progress
Using courses/test/Basics for testing, reveals a bug. When x=2*x is correct but x=3*x is given, x is not restored to its correct value. Debugging.
Fixed #29, locals not restored correctly after incorrect assignment. Missing break in RecordingQuestion.execute
Try to implement variable types in GetValue

This may allow course authors to use any builtin python type as the
desired value in GetValue
Merge branch 'master' into f.shell-resubclass
Changed field name 'values' to 'value' in courses/test/basics.yaml for consistency with code.