clarify distinction between datetime module and class in deprecation messages (again)

Author: neutrinoceros

Lib/_pydatetime.py

@@ -1831,7 +1831,7 @@ def now(cls, tz=None):
     def utcnow(cls):
         "Construct a UTC datetime from time.time()."
         import warnings
-        warnings.warn("datetime.utcnow() is deprecated and scheduled for "
+        warnings.warn("datetime.datetime.utcnow() is deprecated and scheduled for "
                       "removal in a future version. Instead, Use timezone-aware "
                       "objects to represent datetimes in UTC: "
                       "datetime.datetime.now(datetime.UTC).",