Backward compatibility with Python 2.4 (server)

It is often the case that the user has no administrative control over
the server that is being used. As such it is important to support as
many versions as possible, at least on the remote server end. These
fixes will allow sshuttle to be used with servers that have only
python 2.4 or python 2.6 installed while hopefully not breaking the
compatibility with 2.7 and 3.5.

conftest.py

@@ -0,0 +1,10 @@
+import sys
+
+if sys.version_info >= (3, 0):
+    good_python = sys.version_info >= (3, 5)
+else:
+    good_python = sys.version_info >= (2, 7)
+
+collect_ignore = []
+if not good_python:
+    collect_ignore.append("sshuttle/tests/client")