bug#18089: 24.4.50; doc string of `delete-selection-helper'

[Drew Adams <drew.adams@oracle.com>]

1. Mention of the TYPE value `t' is incorrrect.  It should be "non-nil",
   everywhere, based on what the code actually does (and has always done).

2. For FUNCTION, it is not true that the return value should be "one of
   the above values" (even if non-nil replaces t).  The return value can
   apparently also be another FUNCTION.  So the doc string for FUNCTION
   should say that the return value of FUNCTION should be a value
   acceptable as TYPE.

3. All of the info in this doc string should be in the doc string of
   `delete-selection-pre-hook', not in the "helper" function.

4. Doc string lines should be no wider than 70 columns (except the
   first).


In GNU Emacs 24.4.50.1 (i686-pc-mingw32)
 of 2014-06-28 on ODIEONE
Bzr revision: 117431 rgm@gnu.org-20140628015517-eku6hj8mpgcvfnso
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/snapshot/trunk
 --enable-checking=yes,glyphs 'CFLAGS=-O0 -g3'
 LDFLAGS=-Lc:/Devel/emacs/lib 'CPPFLAGS=-DGC_MCHECK=1
 -Ic:/Devel/emacs/include''