bug in factronf()

[Igor Schein <igor@txc.com>]

Hi,

this is a what I call "bad input" bug.
? factornf(x^3+2,y^2-1)
  ***   non-invertible polynomial in polinvmod. \\ correct error message
? factornf(x^3+1,y^2-1)
  ***   the PARI stack overflows !!!

  ***   Warning: doubling stack size; new stack = 8000000.
? factornf(x^3+1,y^2-1)
  ***   the PARI stack overflows !!!

  ***   Warning: doubling stack size; new stack = 16000000.

So factornf() gets confused when both polynomials are reducible and
keeps growing the stack.  This bug was introduced somewhere between
2.0.11.beta and 2.0.12.alpha.

Igor