inconsistency with polynomial factor() in Poly vs LaurentPoly

<div id="comment:0"></div>


```
sage: R.<x> = PolynomialRing(QQ)
sage: (1/(1-x)).factor()
(-1) * (x - 1)^-1
sage: (1-x).factor()
(-1) * (x - 1)

sage: R.<x> = LaurentPolynomialRing(QQ)
sage: (1/(1-x)).factor()
(-1) * (x - 1)^-1
sage: (1-x).factor()
(-1) * (-1 + x)
```


Component: **commutative algebra**

_Issue created by migration from https://trac.sagemath.org/ticket/18082_

