User-defined replacement function can sometimes immediately modify arg

[radfordneal]

In pqR-2014-09-30, user-defined replacement functions can sometimes immediately modify their argument, which is fast, but not entirely safe. For example, after

> `f<-` <- function (x,value) { x[1] <- 1; stop("error") }
> a<-numeric(10); a[1] <- 3; f(a) <- 4
Error in `f<-`(a, value = 4) : error
> a
 [1] 1 0 0 0 0 0 0 0 0 0

we see that a[1] has changed even though the replacement function exited with an error.

This is the result of a combination of a[1] <- 3 letting "a" get a NAMEDCNT of 0, which is generally unnoticeable since it is fixed up later, and invokation of user-defined replacement functions not doing the usual fixup. These problems are now corrected in development branch 30.

[radfordneal]

Now fixed in pqR-2014-10-23.