Build system: Use PHP 5.3 to create pre-built release packages

Otherwise Composer downloads a newer version of Twig which isn't compatible with PHP 5.3. Since we don't pin down specific versions of our dependencies, Composer-based installations might use newer versions of Twig which aren't compatible with PHP 5.3. Raising the PHP requirements requires a new major version, something that will definitly happen with Pico 3.0.

.travis.yml

@@ -25,7 +25,8 @@ jobs:
 
     # Deployment stage
     - stage: deploy
-      php: 5.6
+      php: 5.3
+      dist: precise
       sudo: required
       install:
         - '[ "$TRAVIS_PULL_REQUEST" == "false" ] || travis_terminate 0'