bug#4021: 23.1; X Windows -> X Window

[Drew Adams]

The doc string for `x-set-selection' says this:
 
"Make an X Windows selection of type TYPE and value DATA...."
 
I believe, but I'm no expert on this, that that should be X Window,
not X Windows. If true, and if the same problem appears elsewhere,
then those occurrences should be corrected also.
 
We don't want users to think of X Window and Microsoft Windows as
somehow related. ;-)
 

In GNU Emacs 23.1.1 (i386-mingw-nt5.1.2600)
 of 2009-07-29 on SOFT-MJASON
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.4)'