Note rotating log handler fix in changelog

CHANGES.txt

@@ -6,6 +6,9 @@ Next release
 
 - Removed the unused "supervisor_rpc" entry point from setup.py.
 
+- Fixed a bug in the rotating log handler that would cause unexpected
+  results when two processes were set to log to the same file.
+
 3.0a12 (2011-12-06)
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