Function: poldegree
Section: polynomials
C-Name: gppoldegree
Prototype: GDn
Help: poldegree(x,{v}): degree of the polynomial or rational function x with
 respect to main variable if v is omitted, with respect to v otherwise.
 For scalar x, return 0 if x is non-zero and -oo otherwise.
Doc: degree of the polynomial $x$ in the main variable if $v$ is omitted, in
 the variable $v$ otherwise.

 The degree of $0$ is \kbd{-oo}. The degree of a non-zero scalar is $0$.
 Finally, when $x$ is a non-zero polynomial or rational function, returns the
 ordinary degree of $x$. Raise an error otherwise.
Variant: Also available is
 \fun{long}{poldegree}{GEN x, long v}, which returns \tet{-LONG_MAX} if $x = 0$
 and the degree as a \kbd{long} integer.
