Fixed 2.4 compatibility problem. Added tests to release process to make sure there are no regressions.
diff --git a/Makefile b/Makefile
index e474083..4ae3f1d 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,9 @@
 
 .PHONY: prerelease
 prerelease:
-	python runtests.py --exit_on_failure tests
+	python2.4 runtests.py --exit_on_failure
+	python2.6 runtests.py --exit_on_failure
+	python2.7 runtests.py --exit_on_failure
 	-rm dist/*
 	python setup.py clean
 	python setup.py sdist