[Nauty] nauty&Traces version 2.6r6 released

[Brendan McKay]

Version 2.6r6 is available from the web pages.

Changes:

1. Fixed a rare bug in Traces.  Note that the canonical labelling may 
have changed.  In general, neither nauty nor Traces guarantees that the 
canonical labelling remains the same between versions, as that would 
prevent us from improving them.  The canonical labelling of nauty has 
not changed since version 2.6r1.
2. Fixed shortg for digraphs. The sparse and Traces versions for 
digraphs and all versions for undirected graphs were not affected.
3. Fixed home directory determination in sumlines (which probably 
impacted nobody ever).
4. Disabled automatic popcnt instruction selection for PowerPC processors.

Thanks to Murad Banaji, David Binderman and Jerry James for reporting 
problems.

Brendan and Adolfo.

http://users.cecs.anu.edu.au/~bdm/nauty/
http://pallini.di.uniroma1.it/