bug#12853: 24.2.50; doc of `color-defined-p'

[Drew Adams]

The doc string is missing the most basic information: What data type
parameter COLOR is.  It should say that COLOR must be a string or the
symbol `unspecified' (an error is raised otherwise).
 
It should say that the string can be any string, and that the function
returns non-nil for #1 or #2, and nil otherwise:
 
1. a defined (recognized) color name
2. a color RGB code, with prefix `#'
 
The doc should not say anything about the particular strings
"unspecified-fg" or "unspecified-bg": there is nothing special about
them.  The function returns nil for ANY string other than #1 or #2.
 
Consider adding to the doc string the "Note..." that is in the Elisp
manual and that refers to `color-supported-p'.
 
For the Elisp manual doc of `color-defined-p': change "X" to "X Window".  If the
same bug occurs elsewhere in the manual, please fix those occurrences too.

In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-10-22 on DANI-PC
Bzr revision: 110618 monnier@iro.umontreal.ca-20121022132928-232zm0fecassmhfb
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -I../../libs/libxpm-3.5.8/include -I../../libs/libxpm-3.5.8/src
 -I../../libs/libpng-1.4.10 -I../../libs/zlib-1.2.6
 -I../../libs/giflib-4.1.4-1/include -I../../libs/jpeg-6b-4/include
 -I../../libs/tiff-3.8.2-1/include
 -I../../libs/libxml2-2.7.8-w32-bin/include/libxml2
 -I../../libs/gnutls-3.0.16/include
 -I../../libs/libiconv-1.14-2-mingw32-dev/include'