Configure travis-ci.org tests

Test Django 1.2 and 1.3; Python 2.6 and 2.7

Don't bother testing Python 2.5 -- it requires an older version of
requests (that doesn't depend on json).

Don't bother testing Django 1.2 -- it requires changes to ``assertRaises``
in the test cases (because the context-manager version of assertRaises is
part of unittest2, which appears in Django 1.3+ or Python 2.7+).

Don't bother testing Django 1.5 (yet).

.travis.yml

@@ -0,0 +1,11 @@
+language: python
+python:
+  - "2.6"
+  - "2.7"
+env:
+  - DJANGO_VERSION=1.3
+  - DJANGO_VERSION=1.4
+install:
+  - pip install -q Django==$DJANGO_VERSION
+  - pip install . --use-mirrors
+script: python setup.py test