Fix puiseux._new_polynomial() constant term check.
Fix puiseux._new_polynomial() constant term check.

The Newton polynomial iteration would check if the constant
term disappears. (Every Newton polynomial must have a zero
constant term.) However, Sympy cannot evaluate some
expressions to zero unless symplifying. Simplification is
too expensive to perform on every polynomial coefficient so
it is only performed to validate that the constant term
disappears.

abelfunctions/abelfunctions,abelfunctions/abelfunctions,abelfunctions/abelfunctions,cswiercz/abelfunctions,cswiercz/abelfunctions,cswiercz/abelfunctions