Fix pserve --reload on Py3 (the simple solution)

This is the simpler fix for `pserve --reload` (so please pull either https://github.com/Pylons/pyramid/pull/1244 or this).

Basically with some project setups the reloader thread is guaranteed to crash on Python 3 as the main thread is importing modules in the other thread.
Merge pull request #1245 from ztane/patch-2

Fix pserve --reload on Py3 (the simple solution)
Changelog for PR #1245.
Clarify reasons for preferring easy_install over pip.
Clarify vs. import time.
Avoid re-ambiguating 'project' vs. 'package.
Clarifications.
EC: why not add 'pyramid_debugtoolbar' to our 'install_requires'?
Match optional reqs on Windows to those on POSIX.
Don't leave the page broken.
EC:  break the page and see the DBT traceback display.
Trailing commas are good.
Clarify.