Tub.listenOn: tolerate non-qualified strings like "12345"

Tahoe still uses these, so convert them into "tcp:12345" (which is a
valid endpoint specification) and emit a DeprecationWarning.

src/foolscap/pb.py

@@ -1,6 +1,6 @@
 # -*- test-case-name: foolscap.test.test_pb -*-
 
-import os.path, weakref, binascii
+import os.path, weakref, binascii, re
 from warnings import warn
 from zope.interface import implements
 from twisted.internet import (reactor, defer, protocol, error, interfaces,
@@ -500,6 +500,13 @@ def listenOn(self, what, _test_options={}):
                              "port numbers instead")
             warn(warningString, DeprecationWarning, stacklevel=2)
 
+        if isinstance(what, str) and re.search(r"^\d+$", what):
+            warn("Tub.listenOn('12345') was deprecated "
+                 "in Foolscap 0.12.0; please use qualified endpoint "
+                 "descriptions like 'tcp:12345'",
+                 DeprecationWarning, stacklevel=2)
+            what = "tcp:%s" % what
+
         l = Listener(self, what, _test_options, self.negotiationClass)
         self.listeners.append(l)
         l.setServiceParent(self)

src/foolscap/test/test_listener.py

@@ -53,6 +53,15 @@ def test_parsed_endpoint(self):
         furl = tubA.registerReference(Target())
         yield tubB.getReference(furl)
 
+    @inlineCallbacks
+    def test_nonqualified_port(self):
+        tubA, tubB = self.makeTubs()
+        portnum = util.allocate_tcp_port()
+        tubA.listenOn("%d" % portnum) # this is deprecated
+        tubA.setLocation("tcp:127.0.0.1:%d" % portnum)
+        furl = tubA.registerReference(Target())
+        yield tubB.getReference(furl)
+
     def test_invalid(self):
         tubA, tubB = self.makeTubs()
         self.assertRaises(TypeError, tubA.listenOn, 42)