Improve tox.ini, install py26 for travis.

Signed-off-by: Dan O'Reilly <oreilldf@gmail.com>

python/tox.ini

diff --git a/python/tox.ini b/python/tox.ini
index 4a994b6..ebe7545 100644
--- a/python/tox.ini
+++ b/python/tox.ini
@@ -2,17 +2,20 @@
 envlist =
     # Py3 tests currently fail because of text handling issues,
     # So only test py26/py27 for now.
-    #py26,py27,py33,py34
-    py26,py27
+    #py{26,27,33,34}-{cpp,python}
+    py{26,27}-{cpp,python}
 
 [testenv]
-usedevelop = true
 setenv =
-    LD_LIBRARY_PATH={toxinidir}/../src/.libs
+    cpp: LD_LIBRARY_PATH={toxinidir}/../src/.libs
+    cpp: PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=cpp
 commands =
     python setup.py -q build_py
-    python setup.py -q build {posargs}
-    python setup.py -q test -q {posargs}
-    pip install --install-option {posargs: -q} .
+    python: python setup.py -q build
+    cpp: python setup.py -q build --cpp_implementation
+    python: python setup.py -q test -q
+    cpp: python setup.py -q test -q --cpp_implementation
 deps =
     six
+    py26: ordereddict
+    py26: unittest2