very cute bug

[Igor Schein <igor@txc.com>]

Hi, I discovered the following bug ( a,b and c are undefined):
? printp(1/a+1/b+1/c)
  ***   segmentation fault: bug in GP (please report).

At this point, gp has gone mad and gives segfault on
any output, so one must exit.

I only tested this on Solaris ( both 2.0.11 and 2.0.12), 
so I don't know if other platforms are vulnerable.   I'll
do some debugging, if time permits

Igor