[Nauty] showg fixed

[Brendan McKay]

Gordon Royle kindly pointed out that the stand-alone reader showg
did not work for digraphs.  It is now hopefully fixed.  The following
new packages differ from their predecessors only in that aspect:

nauty26r9.tar.gz = production release
nauty27b6.tar.gz = beta version

Note that listg can do everything that showg can do and more, so if
you are installing the whole package you should just ignore showg.
However, showg can be compiled by itself so it is useful for people
who just want to decode graph files.

Now I need a little help.  At
     http://users.cecs.anu.edu.au/~bdm/data/formats.html
there is the new source code for showg.c and some pre-compiled
executables.  I have not been able to compile the versions for
32-bit Linux and 32-bit Windows.  If anyone can manage one or
both of those, please send me the executable and I'll install it.
In both cases static linking (-static for gcc) ensures maximum
portability, and architecture as generic as possible is good. Thanks.

Brendan.