Function: pollead
Section: polynomials
C-Name: pollead
Prototype: GDn
Help: pollead(x,{v}): leading coefficient of polynomial or series x, or x
 itself if x is a scalar. Error otherwise. With respect to the main variable
 of x if v is omitted, with respect to the variable v otherwise.
Description:
 (pol):gen:copy         leading_coeff($1)
 (gen):gen              pollead($1, -1)
 (gen, var):gen         pollead($1, $2)
Doc: leading coefficient of the polynomial or power series $x$. This is
  computed with respect to the main variable of $x$ if $v$ is omitted, with
  respect to the variable $v$ otherwise.
