Use virtualenv for all builds and install everything from wheelhouse

Use venv for all builds and install everything from wheelhouse

Use venv and all minimum requirements

Edit requirements.txt in place and use one call

Update minimum versions and install exclusively from wheelhouse

Use mpl 1.3.1 on py 3.2

Fix pip invocation

Fix pip invocation again

Another fix to pip invocation

Explicitly use venv python to call build_versions.py

Move venv creation and activation to top level

Do not use site-packages

Fix minimum matplotlib ver and Pillow version check

Fix minimum matplotlib ver

Improve error message on version check

Add more debug info

Even more debug info

More debug info

Yet another debug print

Fix python 2.7 installation problem

check for PIL.Image version on install

Add debug to before_install

Try a pip install virtualenv first

Clean up virtualenv creation, add debug info, fix PySide script install

Fix virtualenv path for PySide install

Fix venv location and activation

Try no site packages and fix python 2.7 install
Use system packages on Py2.7

Use system packages on python 2.7

Try and fix PyQt4 and use wheelhouse astropy

Fix version requirements
Clean up use of python version check for pyqt install
Fix python version check
Invoke sudo to create link to system PyQt
Merge pull request #1253 from blink1073/travis-venv

Use new Virtual Environments for Travis