#4962 bfallroots fails on polynomials with multiple roots

[David Scherfgen]

bfallroots reports "no roots found" where allroots succeeds, and raising fpprec turns success into failure

Maxima 5.49post, SBCL 2.6.7.

(%i1) display2d:false$
(%i2) p: x^3-3*x^2+3*x-1$   /* (x-1)^3 */
(%i3) allroots(p);
(%o3) [x = 1.0,x = 1.0,x = 1.0]
(%i4) fpprec:34$ bfallroots(p);
(%o4) [x = 1.02216594161483846800669072150833b-11*%i+9.99999999989775609083821176835b-1, ...]
(%i5) fpprec:35$ bfallroots(p);
bfallroots: no roots found.
(%i6) fpprec:40$ bfallroots(x^4-8*x^3+24*x^2-32*x+16);   /* (x-2)^4 */
bfallroots: no roots found.
(%i7) bfallroots(x^4+2*x^2+1);                            /* (x^2+1)^2 */
bfallroots: no roots found.

Expected: the roots, as allroots returns for all three polynomials.

fpprec 34 succeeds on (x-1)^3 and 35 fails, so asking for more digits makes a working call stop working.