Log message:
Mark packages as not ready for python-3.x where applicable;
either because they themselves are not ready or because a
dependency isn't. This is annotated by
PYTHON_VERSIONS_INCOMPATIBLE=  33 # not yet ported as of x.y.z
or
PYTHON_VERSIONS_INCOMPATIBLE=  33 # py-foo, py-bar
respectively, please use the same style for other packages,
and check during updates.

Use versioned_dependencies.mk where applicable.
Use REPLACE_PYTHON instead of handcoded alternatives, where applicable.
Reorder Makefile sections into standard order, where applicable.

Remove PYTHON_VERSIONS_INCLUDE_3X lines since that will be default
with the next commit.

Whitespace cleanups and other nits corrected, where necessary.

Log message:
Import py27-doctor-0.4 as devel/py-doctor.

This is 'pydoctor', an API documentation generator that works by
static analysis.

It was written primarily to replace epydoc for the purposes of the
Twisted project as epydoc has difficulties with zope.interface.  If it
happens to work for your code too, that's a nice bonus at this stage :)

pydoctor puts a fair bit of effort into resolving imports and
computing inheritance hierarchies and, as it aims at documenting
Twisted, knows about zope.interface's declaration API and can present
information about which classes implement which interface, and vice
versa.