error.LookupError: rename 'message' property to something else

At least some installs of Python 2.6+ complain with:

    mercurial/error.py:26: DeprecationWarning: BaseException.message has been
        deprecated as of Python 2.6

This patch renames the property away from 'message' so that Python no longer
complains.

mercurial/error.py

@@ -23,7 +23,9 b' class LookupError(RevlogError, KeyError)'
     def __init__(self, name, index, message):
         self.name = name
         self.index = index
-        self.message = message
+        # this can't be called 'message' because at least some installs of
+        # Python 2.6+ complain about the 'message' property being deprecated
+        self.lookupmessage = message
         if isinstance(name, str) and len(name) == 20:
             from node import short
             name = short(name)