Add py3-* packages for toposort and pyPEG2.

[ed]

Summary

The port for ARPC (https://github.com/NuxiNL/arpc) I am preparing comes
with a script called 'aprotoc' that depends on these Python modules.
Ports that default to Python 2 have already been added, but now we
should add Python 3 flavours as well.

[koobs]

Looks OK, pending confirmation that port passes QA (poudriere w/ Python 3.x)

[ed]

In D12068#252037, @koobs wrote:

Looks OK, pending confirmation that port passes QA (poudriere w/ Python 3.x)

Just double checked using Poudriere. Logs can be found here: http://80386.nl/pub/latest-per-pkg/