add a tox.ini

setup.py dev

Non-user-facing: setup.py dev in pip checkout will run setup.py develop and then cause test_requires requirements to be installed

Fixing import error for tempfile

A change was made to add extra logging whenever pip log files cannot be added. 

Here is the changeset that caused the issue:  https://github.com/pypa/pip/commit/8ebc7a316016c4eb01cb77c8df1fe538c7bddf2a#pip/basecommand.py

Issue 656   just log warning when no uninstall paths, don't raise error

Also show the full path in the missing command error message.