groups/types.py: Gave `group` an `isSubset` method
Fixed a stupid bug.  I need to add unit testing.
C++: Changed `AutCyclic::contains` to use `gcd` instead of `binary_search`,
which should be faster (Why did I ever use `binary_search` for this in the
first place?).  Also found & fixed an issue with AutCyclic(1).