A couple of simple optimizations
A couple of simple optimizations

Weirdly, copy.deepcopy of a set of str is much slower than just
creating a new set - maybe because it is also copying the strings?
But there is no need for that because while we edit the set we don't
edit any members. Saves about 1.5 seconds on Pi2.

randombit/botan,webmaster128/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,randombit/botan,randombit/botan,randombit/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan,randombit/botan,webmaster128/botan,webmaster128/botan,Rohde-Schwarz-Cybersecurity/botan,Rohde-Schwarz-Cybersecurity/botan,webmaster128/botan