#889 simplification of x^2/x yields x (ignores zero value)

[Robert Dodier]

Simplification of x^2/x yields x, although that is not
valid when x = 0.

Other examples involving polynomials are easy to
construct, e.g, (x - 1)^2/(x - 1) => x - 1, (x - 1)*(x
+ 1)/(x - 1) => x + 1. Dunno if quotient
simplifications include other kinds of expressions.

Perhaps simplification of quotients could yield
unevaluated conditionals, e.g., something like x^2/x =>
if x # 0 then x else undefined(x^2/x); or (assume(not
equal(x, 0)), x^2/x) => x.