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, which is converted to distribute in py3)
- `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