Add py-topoosort and py3-toposort.

[ed]

Summary

I am currently in the process of creating ports for various components
related to CloudABI, including ARPC (an RPC framework that supports file
descriptor passing) and Flower (a capability-based network backplane).

The former comes with a script called 'aprotoc' for creating C++
bindings for messages and RPC services. This script depends on Python's
toposort package to order declarations in the resulting C++ header file,
taking dependencies into account.

[ed]

Revert premature change to devel/Makefile.

[ed]

Add a proper pkg-descr.

Sorry for the noise.

[wg]

LGTM

[ed]

Wow! Thanks for reviewing this change so quickly!

When I tried committing this, I got an error message, regarding py3-* ports being deprecated in favour of FLAVORS support. I've removed the py3-toposort port from this change and went ahead committing this.

[koobs]

Adding py3-* ports requires an Approved by: portmgr (user) line in the commit (to bypass the pre-commit gate)

Mat is a member of portmgr though its not explicit with what hat he accepted (assume not portmgr unless explicit)

If you need py3-toposort as a dependency for another port that uses it (and builds with Python 3.x), just create a new review and add portmgr (Blocking) to reviewers