Add requirements files for our optional dependencies and test with them.

Author: gsnedders

.travis.yml

@@ -6,14 +6,20 @@ python:
   - "3.3"
   - "pypy"
 
+env:
+  - USE_OPTIONAL=true
+  - USE_OPTIONAL=false
+
 before_install:
   - git submodule update --init --recursive
 
 install:
   - pip install -r requirements.txt -r requirements-test.txt --use-mirrors
+  - if [[ $USE_OPTIONAL == "true" ]]; then pip install -r requirements-optional.txt --use-mirrors; fi
+  - if [[ $TRAVIS_PYTHON_VERSION != "pypy" && $USE_OPTIONAL == "true" ]]; then pip install -r requirements-optional-cpython.txt --use-mirrors; fi
 
 script:
   - nosetests
 
 after_script:
-  - python debug-info.py
+  - python debug-info.py

requirements-optional-cpython.txt

@@ -0,0 +1,3 @@
+# lxml is supported with its own treebuilder ("lxml") and otherwise
+# uses the standard ElementTree support
+lxml

requirements-optional.txt

@@ -0,0 +1,11 @@
+# We support a Genshi treewalker that can be used to serialize Genshi
+# streams.
+genshi
+
+# chardet can be used as a fallback in case we are unable to determine
+# the encoding of a document.
+chardet
+
+# DATrie can be used in place of our Python trie implementation for
+# slightly better parsing performance.
+datrie