Fix for "pip" detection so that setuptools is used

I am no "expert" with pip deployment, but this bug seems rather obnoxious.
If there is a better way to detect the usage of pip, please reject this pull request
and use it instead.  I do think that pip installation should not require the exporting
of env variables to be successful.

The issue appears on 12.04 Ubuntu and OS X for sure.  I am sure we will see it other places as well.

---- Commit message Start ---

If setuptools is not used for PIP installs pip fails to install salt
with a rather nasty error:

error: option --single-version-externally-managed not recognized

from what I can dig up the simple use of:
    if "pip" in __file__

is sufficient to detect pip usage, and should be synonomous
with USE_SETUPTOOLS