Bugfix issue #104: an SSL unwrap() sends data, and so it needs trampolining.

Be warned that I do not quite understand what makes certain SSL operations
"gross" (in the terminology of ssl.py's comments) and require the methods to
be copied wholesale into the GreenSSLSocket; but simply adding the trampoline
like this works for me!

eventlet/green/ssl.py

@@ -185,7 +185,8 @@ class GreenSSLSocket(__ssl.SSLSocket):
         return super(GreenSSLSocket, self).recvfrom_into(buffer, nbytes, flags)
 
     def unwrap(self):
-        return GreenSocket(super(GreenSSLSocket, self).unwrap())
+        return GreenSocket(self._call_trampolining(
+                super(GreenSSLSocket, self).unwrap))
 
     def do_handshake(self):    
         """Perform a TLS/SSL handshake."""