Need to include current directory too, I think.

Makefile

@@ -61,13 +61,14 @@ travistest:
 	make bench
 
 # combine after each step so we don't lose anything (append is the default). This also
-# moves the coverage file from greentest to the root.
+# moves the coverage file from greentest to the root. It's necessary to specify the current
+# directory to include all results previously combined too.
 	cd greentest && GEVENT_RESOLVER=thread ${PYTHON} testrunner.py --config ../known_failures.py
-	coverage combine greentest/
+	coverage combine . greentest/
 	cd greentest && GEVENT_RESOLVER=ares GEVENTARES_SERVERS=8.8.8.8 ${PYTHON} testrunner.py --config ../known_failures.py --ignore tests_that_dont_use_resolver.txt
-	coverage combine greentest/
+	coverage combine . greentest/
 	cd greentest && GEVENT_FILE=thread ${PYTHON} testrunner.py --config ../known_failures.py `grep -l subprocess test_*.py`
-	coverage combine greentest/
+	coverage combine . greentest/
 
 toxtest:
 	cd greentest && GEVENT_RESOLVER=thread python testrunner.py --config ../known_failures.py