Overriding _stub_task to preserve due date; display the actual error message when a task is not creatable.
Merge branch 'fix_date_serialization' into inthe_am

Conflicts:
	taskw/warrior.py
Use string_types rather than basestring.
Removing unicode literal.
Use six.text_type rather than a unicode literal.
Use string_types rather than basestring.
Use six.text_type rather than a unicode literal.
Merge branch 'fix_date_serialization' into inthe_am
Merge branch 'fix_annotation_handling' into inthe_am

Conflicts:
	taskw/test/test_utils.py
	taskw/utils.py