gp: forbidden multiplication t_INT * t_RFRAC

[Michael Somos <somos@grail.cba.csuohio.edu>]

This is a bug in division which may have been triggered by not reducing
properly a rational fraction. Note that the first example without the
minus sign is okay. The second example with the '1/Ser(...)' is okay also.
However, the third example which first does the 'Ser(...)' and then the
reciprocal triggers the bug.

==============================================================================
Reading GPRC: /u/home/somos/.gprc ...Done.

          GP/PARI CALCULATOR Version 2.2.4 (development CHANGES-1.491)
                 UltraSparc (MicroSparc kernel) 32-bit version
              (readline v2.2 enabled, extended help not available)

                       Copyright (C) 2002 The PARI Group

PARI/GP is free software, covered by the GNU General Public License, and 
comes WITHOUT ANY WARRANTY WHATSOEVER.

Type ? for help, \q to quit.
Type ?12 for how to get moral (and possibly technical) support.

   realprecision = 28 significant digits
   seriesprecision = 16 significant terms
   format = g0.28

parisize = 4000000, primelimit = 500000
? [1/y,1/(y+z)]
%1 = [1/y, 1/(y + z)]
? Ser(%/%[1])
%2 = 1 + y/(y + z)*x + O(x^2)
? 1/%
%3 = 1 - y/(y + z)*x + O(x^2)
? [-1/y,1/(y+z)]
%4 = [-1/y, 1/(y + z)]
? 1/Ser(%/%[1])
%5 = 1 + y/(y + z)*x + O(x^2)
? [-1/y,1/(y+z)]
%6 = [-1/y, 1/(y + z)]
? Ser(%/%[1])
%7 = 1 + y/(-y - z)*x + O(x^2)
? 1/%
  ***   forbidden multiplication t_INT * t_RFRAC.
? quit
Goodbye!
==============================================================================

Shalom, Michael