[with patch] fraction field __pow__ doesn't handle negative exp. elegantly

[jbmohler]

Negative exponents put fraction field elements in the denominator of a fraction field element.

sage: R.<x>=ZZ[]
sage: (1/x)^-3
1/(1/x^3)

With the patch:

sage: R.<x>=ZZ[]
sage: (1/x)^-3
x^3

[was]

It looks good to me except change the somewhat too verbose

  sage: x = PolynomialRing(RationalField(),'x').gen() 

to one of the following (take your pick):

  sage: x = polygen(QQ, 'x')

or

  sage: R.<x> = QQ[]

or

  sage: x = PolynomialRing(QQ,'x').gen()

I think it is important that the docstrings give illustrations of good usage of Sage.

[mhansen]

This is a duplicate of #1786. I didn't realize that this was indeed the issue when opening #1786.