don't install or build wheels for distribute in python 3

a solution for #891 and #650

for example, users currently can't do either of these practical commands in py3 without failing with distribute 2to3 related errors, due to pyramid depending on setuptools
- `pip wheel pyramid`
- `pip install -U pyramid`

the change:
 - in py3, skip "distribute" for wheel building or installs.
 - uses get a notify message of the skip

I think it's acceptable to just declare that in py3, pip can not reinstall/downgrade/upgrade distribute.  I can followup with some changes to the docs to explain the situation, and how they could do it manually.

this problem will go away after the setuptools/distribute merge, due to the new setuptools having py2-py3 compatible code that does not require 2to3