psPolynomial using nTerms not nOrder

[eugene]

psPolynomial functions are all implemented using the convention psPolynomial.n
is the number of terms, not the number of orders (ie, a line requires n = 2, not
n = 1). This should be implemented as 'number of orders' instead (ie, line
should be specified using n = 1). The SDRS v.15 was a bit ambiguous: the text
said orders, but the comments in the code blocks said 'terms'.

[Paul Price]

Ditto with psPlaneTransform: it currently takes the number of terms, not the
polynomial orders. I changed the SDRS to make it clearer:

Each of \code{psPlaneTransform} and \code{psPlaneDistort} has an
appropriate allocator that takes the polynomial order in each
dimension. Both the \code{x} and \code{y} polynomials shall be have
the same dimensions.
\begin{prototype}
psPlaneTransform *psPlaneTransformAlloc(int order1, int order2);
psPlaneDistort *psPlaneDistortAlloc(int order1, int order2, int order3, int order4);
\end{prototype}

(Previously had "n1, n2" as the arguments.)

[gusciora@…]

Done.