Change in factor behavior between 1.2 and 1.3

[dv-brianmickel]

factor((x^3+x^2+x)*(y^3+y^2),x,y)
#v1.2.0: -> x*y^2*(x^2+x+1)*(y+1)
#v1.3.1: -> 0

Bug introduced in the code changes in this commit (builds in the next commit)
358e699

works as expected in the previous commit: 053ee01
broken in cd0ea4d