Add PyPy testing to Travis CI

.travis.yml

@@ -6,12 +6,14 b' python:'
     - 3.4
     - 3.3
     - 2.7
+    - pypy
 sudo: false
 before_install:
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
     - 'if [[ $GROUP != js* ]]; then COVERAGE=""; fi'
 install:
     - pip install "setuptools>=18.5"
+    - if [ $TRAVIS_PYTHON_VERSION == pypy ] ; then pip install https://bitbucket.org/pypy/numpy/get/pypy-4.0.1.zip ; fi
     - pip install -f travis-wheels/wheelhouse -e file://$PWD#egg=ipython[test]
     - pip install codecov
 script:
@@ -23,4 +25,5 b' after_success:'
 
 matrix:
     allow_failures:
-        python: nightly
+        - python: nightly
+        - python: pypy