Update bootstrap.py to newest version.
Plone 4.1 tests: use dexterity pinnings.

Dexterity is not included in Plone 4.1's version pinnings,
therefore we also include the dexterity KGS for having compatible dexterity packages.
Update travis config: use a completely isolated python.

Travis has already an older setuptools version installed in
the site packages.  By using --no-site-packages and
--no-setuptools we get a completely isolated python and can
install whathever versions of setuptools the bootstrap.py
requires.
Merge pull request #40 from collective/jone-fix-tests

Fix test setup