bug#2391: 23.0.90; doc string of keymap-parent

[Drew Adams]

Doc string:
 
"Return the parent keymap of KEYMAP."
 
And what if KEYMAP has no parent?
 
It should say what the Elisp manual says:
 
"This returns the parent keymap of KEYMAP.  If KEYMAP has no
parent, `keymap-parent' returns `nil'."
 
IOW, it should say this:
 
"Return the parent keymap of KEYMAP, or nil if KEYMAP has no parent."
 
 
 
In GNU Emacs 23.0.90.1 (i386-mingw-nt5.1.2600)
 of 2009-02-01 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'