pbeta() -> bratio() no longer overflows for pbeta(., <large>, <large>)

git-svn-id: https://svn.r-project.org/R/trunk@88248 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: maechler

doc/NEWS.Rd

@@ -152,6 +152,11 @@
       \item \code{prettyNum(*, zero.print={>=1-char}, replace.zero=TRUE)}
       now works as documented, thanks to Marttila Mikko and Ivan Krylov's
       messages on R-devel.
+
+      \code{pbeta(x, a,b, ..)} for very large \code{a,b} no longer returns
+      \code{NaN} but the correct values (0 or 1, or their logs for \code{log.p = TRUE}).
+      This improves Mathlib's C level \code{bratio()} and hence also
+      \code{pnbinom()}, etc..
     }
   }
 }