Function: rnfisfree
Section: number_fields
C-Name: rnfisfree
Prototype: lGG
Help: rnfisfree(bnf,x): given an order x as output by rnfpseudobasis or
 rnfsteinitz, outputs true (1) or false (0) according to whether the order is
 free or not.
Doc: given $\var{bnf}$ as output by
 \kbd{bnfinit}, and either a polynomial $x$ with coefficients in $\var{bnf}$
 defining a relative extension $L$ of $\var{bnf}$, or a pseudo-basis $x$ of
 such an extension, returns true (1) if $L/\var{bnf}$ is free, false (0) if
 not.
