Correct gammavariate's method name and domain.

Partial solution to SF bug 527139.

Doc/lib/librandom.tex

@@ -216,9 +216,9 @@ these equations can be found in any statistics text.
   positive infinity.
 \end{funcdesc}
 
-\begin{funcdesc}{gamma}{alpha, beta}
+\begin{funcdesc}{gammavariate}{alpha, beta}
   Gamma distribution.  (\emph{Not} the gamma function!)  Conditions on
-  the parameters are \code{\var{alpha} > -1} and \code{\var{beta} > 0}.
+  the parameters are \code{\var{alpha} >= 0.5} and \code{\var{beta} > 0}.
 \end{funcdesc}
 
 \begin{funcdesc}{gauss}{mu, sigma}