Update tests for Travis updates

Use postgresql-9.1-postgis-2.0
Use native Python and PIP
Update tests
Rm Travis backports
Update to buildout 2
New validations rules
Travis don't use buildout
Merge pull request #204 from sbrunner/tests

Update tests for Travis updates …
Rework // prevention in base urls

We now:
1. process substitutions;
2. add a '/' at end of urls if missing.

This way we should avoid creating '//' situations.
Exit with error on script fail