BLD: add xlrd, openpyxl installation to travis build

Author: y-p

.travis.yml

@@ -29,7 +29,7 @@ install:
   - 'if [ $TRAVIS_PYTHON_VERSION == "3.3" ]; then pip uninstall numpy; pip install https://github.com/numpy/numpy/archive/v1.7.0b2.tar.gz; fi'
   - 'if [ $TRAVIS_PYTHON_VERSION == "3.2" ] || [ $TRAVIS_PYTHON_VERSION == "3.1" ]; then pip install https://github.com/y-p/numpy/archive/1.6.2_with_travis_fix.tar.gz; fi'
   - 'if [ ${TRAVIS_PYTHON_VERSION:0:1} == "2" ]; then pip install numpy; fi' # should be nop if pre-installed
-  - pip install --use-mirrors cython nose pytz python-dateutil;
+  - pip install --use-mirrors cython nose pytz python-dateutil xlrd openpyxl;
 
 script:
    - python setup.py build_ext install