doc string of compilation-next-error

[Drew Adams]

Shouldn't the doc string mention what the return value is?  At least
one use of the function in the Emacs source code makes use of this
value:

  (let* ((columns compilation-error-screen-columns) ; buffer's local value
         (last 1)
         (loc (compilation-next-error (or n 1) nil
                                      (or compilation-current-error
                                          compilation-messages-start
                                          (point-min))))
         (end-loc (nth 2 loc))
         (marker (point-marker)))
    ...)


In GNU Emacs 22.0.96.1 (i386-mingw-nt5.1.2600)
 of 2007-03-21 on LENNART-69DE564
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --cflags -Ic:/g/include'