Added another check in the spin.copy unit test 'test_copy_fail'.
Bug fixes for the spin.copy() unit test 'test_copy_between_residues'.
Fixed a number of bugs in the generic_fns.spin unit test setup_data function.
Fixed a small bug in the spin.copy() unit test 'test_copy_between_residues'.
Fixes to the spin.copy() unit test 'test_copy_between_molecules'.
More fixes for the data setup for the spin.copy() unit function tests.
Fixed up the data setup for the spin.copy() unit function tests.
Added a docstring and comments to the selection class method __contains__().
Added the missing return_spin import.
Created the function generic_fns.selection.return_spin().