Improved build matrix.

The build is now testing using the latest django patch version for each major version.
Travis will now retry installing python dependecies if there's a network error.

.travis.yml

@@ -6,24 +6,24 @@ python:
   - "3.3"
   - "3.4"
 env:
-  - DJANGO="django==1.4.2"
-  - DJANGO="django==1.5.1"
-  - DJANGO="django==1.6.0"
-  - DJANGO="django==1.7.0"
+  - DJANGO="django>=1.4.0,<1.5.0"
+  - DJANGO="django>=1.5.0,<1.6.0"
+  - DJANGO="django>=1.6.0,<1.7.0"
+  - DJANGO="django>=1.7.0,<.1.8.0"
 matrix:
   exclude:
   - python: "2.6"
-    env: DJANGO="django==1.7.0"
+    env: DJANGO="django>=1.7.0,<1.8.0"
   - python: "3.2"
-    env: DJANGO="django==1.4.2"
+    env: DJANGO="django>=1.4.0,<1.5.0"
   - python: "3.3"
-    env: DJANGO="django==1.4.2"
+    env: DJANGO="django>=1.4.0,<1.5.0"
   - python: "3.4"
-    env: DJANGO="django==1.4.2"
+    env: DJANGO="django>=1.4.0,<1.5.0"
 
 install:
-  - pip install -q coveralls  # installs coverage
-  - pip install $DJANGO
+  - travis_retry pip install -q coveralls  # installs coverage
+  - travis_retry pip install $DJANGO
   - pip install -e .
 
 script: