[Nauty] nauty and traces version 2.6r3 available

[Brendan McKay]

Nauty and traces version 2.6r3 are available at the usual places.

Changes:
* Some corrections to the manual.
* The software license is now Apache 2.0.
* A few very minor tweaks.

A note: The sparse version of nauty, and also Traces, do not sort the 
adjacency
lists of the canonical graph.  If you want them sorted, call 
sortlists_sg( ) as well.
The manual now correctly reports this behaviour.  The reason that sorting is
not done by default is that sometimes it takes quite a long time. For 
example,
for random graphs with 1000 vertices, sorting the adjacency lists takes 5-6
times as long as finding the canonical graph without sorting.

Brendan.