issue #275: default to 'python' for default remote interpreter.

So we get 2.4/2.5/2.6/2.7/3.x.

mitogen/parent.py

@@ -648,7 +648,7 @@ class Stream(mitogen.core.Stream):
     Base for streams capable of starting new slaves.
     """
     #: The path to the remote Python interpreter.
-    python_path = 'python2.7'
+    python_path = 'python'
 
     #: Maximum time to wait for a connection attempt.
     connect_timeout = 30.0