bug#16942: 24.3; replace-match does not return t as stated in the manual

[Glenn Morris]

Version: 24.4

Phillip Lord wrote:

>>From info node: `(elisp) Replacing Match' 
>
>      If you did the last search in a buffer, you should omit the STRING
>      argument or specify `nil' for it, and make sure that the current
>      buffer is the one in which you performed the last search.  Then
>      this function edits the buffer, replacing the matched text with
>      REPLACEMENT.  It leaves point at the end of the replacement text,
>      and returns `t'.
>     
> In my hands, replace-match returns nil regardless. The docstring does
> not mention the return type.

I simply undocumented the return value, since it was both uninteresting
and wrong.