bug#12912: 24.3.50; doc string for `read-face-name'

[Drew Adams]

This doc seems to be incomplete and unclear wrt DEFAULT.
 
It speaks of a case where DEFAULT is not a string.  It does not say what
else it must/can be (besides nil).  Can it be a symbol - e.g., a face
symbol?  Can it be a list of strings, i.e., multiple defaults?  A list
of faces (symbols)?
 
What's more, there is nothing in the doc string that indicates that the
face name(s) is/are read using `completing-read-multiple'.  Not that
that implementation detail need be mentioned explicitly, but its
_behavior_, i.e., what the behavior of `read-face-name' is, should be
described.
 
In GNU Emacs 24.3.50.1 (i386-mingw-nt5.1.2600)
 of 2012-11-05 on MS-W7-DANI
Bzr revision: 110809 lekktu@gmail.com-20121105172930-a5gn0bwi4lndchhw
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -I../../libs/libXpm-3.5.10/include -I../../libs/libXpm-3.5.10/src
 -I../../libs/libpng-1.2.37-lib/include -I../../libs/zlib-1.2.5
 -I../../libs/giflib-4.1.4-1-lib/include
 -I../../libs/jpeg-6b-4-lib/include
 -I../../libs/tiff-3.8.2-1-lib/include
 -I../../libs/libxml2-2.7.8-w32-bin/include/libxml2
 -I../../libs/gnutls-3.0.9-w32-bin/include
 -I../../libs/libiconv-1.9.2-1-lib/include'