Revert "Drop dependency on greenlet/etc for Python3, as swift module is not yet"

This reverts commit 44ae6443748139ee21843b6bdd537edb310c9484.

.travis.yml

@@ -9,9 +9,9 @@ matrix:
     - python: "pypy"
       env: TEST_REQUIRE="fastimport"
     - python: "3.4"
-      env: TEST_REQUIRE="fastimport"
+      env: TEST_REQUIRE="gevent greenlet geventhttpclient fastimport"
     - python: "3.5"
-      env: TEST_REQUIRE="fastimport"
+      env: TEST_REQUIRE="gevent greenlet geventhttpclient fastimport"
 cache:
   directories:
     - $HOME/.cache/pip