Log Message:
Some compilers (e.g. Sunpro) emit one char[] per string, even when
multiple identical strings appear in a source file.
As a result, comparing char *o to the "" pointer gives the wrong result
in vis.c, as the "" pointer we're checking against isn't the same as the
"" which initialised char *o.
Use a global pointer initialised to "", and use it for MAKEEXTRALIST()
calls.
Thanks to Christos Zoulas for suggesting the right solution :)