Travis: record some basic information about the build platform

The question has come up sometimes about how much memory etc. we have available for Travis builds. Let's just log the relevant resource limits at the top of every build log.

.travis.yml

@@ -13,6 +13,10 @@ matrix:
     - python: 3.2
       env: NPY_SEPARATE_COMPILATION=0
 before_install:
+  - uname -a
+  - free -m
+  - df -h
+  - ulimit -a
   - mkdir builds
   - pushd builds
   - pip install nose