test with and without LXML

.travis.yml

@@ -4,10 +4,15 @@ python:
   - "3.3"
   - "2.7"
   - "2.6"
+
+env:
+    - LXML=true
+    - LXML=false
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
 # install: PLEASE CHANGE ME
 install:
-    pip install coveralls --use-mirrors
+    - pip install coveralls --use-mirrors
+    - if $LXML == true; then pip install --use-mirrors lxml; fi
 
 # command to run tests, e.g. python setup.py test