Issue #6: Fixed PyPy 3 compatibility in the test suite by adding a de…

…vice_encoding() function to the mock os library

src/zc/lockfile/tests.py

@@ -33,6 +33,10 @@ def getpid(self):
     def gethostname(self):
         return 'myhostname'
 
+    def device_encoding(self, fd):
+        """In PyPy3, os.device_encoding() is called when acquiring a lock"""
+        return None
+
 os_socket_mock = OsSocketMock()