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 …
Add an error message
Merge pull request #203 from sbrunner/error-message

Add an error message
Exit with error on script fail
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.
Merge pull request #202 from gberaudo/master

More work on double slashes prevention
Start version 0.9.0
Add missing requirements.txt in the package
Merge branch '0.8'
Don't specify nose version
Merge pull request #206 from sbrunner/nose

Don't specify nose version
Don't specify nose version
Merge remote-tracking branch 'origin/0.8'
Fix default http_url for filesystem cache
Typo
Have one error files per layer