This commit decouples the test virtualenv creation from tox and simplify
it for running both locally and on travis-ci. Creation of the test
virtualenvs now happen via Makefile target 'test-env' which will create
2 virtualenvs in the dir tests/virtualenvs and also dump their
respective package data in .pickle files that will be used by the tests.
Also, builds on travis now no longer depend on tox but reuses some of
the Makefile targets for test virtualenv creation/cleanup.
The pickle files for test virtualenv data were created using an older
version of pip. As tox started using the newer version of pip, these
files were obsolete and it lead to failure of tests run via tox. This is
now fixed by regenerating the pickle files for pip ver. 6.0.8
Tom Terrace