[COMMIT] Don't share a counter when checking for circularity, list_merge().

[Aidan Kehoe]

 Ar an dara lá déag de mí Deireadh Fómhair, scríobh Robert Pluim: 

 > On Tue, Oct 12, 2010 at 7:37 PM, Aidan Kehoe <kehoea at parhasard.net> wrote:
 > >
 > > From eyeballing the code, the bug seems to be that my circularity
 > > checking in list_merge() wasn’t done correctly. The below fixes a
 > > related error that I can reproduce easily; could I ask you to apply it
 > > locally and tell me if it fixes your error, too?
 > 
 > Yes. Commit away :)
 > 

OK.

APPROVE COMMIT

NOTE: This patch has been committed.

[...]

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