Extending interfaces of:
 * assertTraitChanges
 * assertTraitDoesNotChange

adding
 * assertMultiTraitChanges
Restoring deleted code
restoring deleted doc strings
more docstring fixes
Lets not review whitespace changes
restoring deleted test code
Updating documentation based on suggestions.
Fixing errorneous docstring.
Merge pull request #53 from enthought/feature-extended-test-helpers

Extending various trait testing helpers