[Cbc] CbcSymmetry in trunk

[John Forrest]

I probably should say something about the code that I eventually checked 
in to Cbc/trunk.

Highly symmetric problems are difficult for Branch and Bound, so codes 
have symmetry breaking code.  I have implemented Orbital Branching as 
described in papers by Ostrowski et al.  I hacked some code from Couenne 
and then put my own spin on it.  Orbital Branching can be expensive and 
I have just had a first pass at it.  It uses nauty code (which stands 
for No AUTomorphisms Yes) - not naughty code.

Adventurous people can try it out - see CbcSymmetry.hpp for some help.

It is a first pass - anyway it is not normally switched on.

John Forrest