bug#9675: 24.0.50; doc for font name specification

[Drew Adams]

(elisp) Low-Level Font says this about `font-spec' keyword `:name':
 
 The font name (a string), in either XLFD, Fontconfig, or GTK
 format.  *Note Font Specification Options: (emacs)Font X.
 
There is no explanation or cross reference to understand what those 3
formats are, and without that info this description is useless.  The
cross ref that is there takes you to a node about font specification on
the command line (for X Window only?).
 
Please _specify_ the available formats for the `:name' value.  Or if
they are in fact already clearly specified somewhere, then please cross
reference that/those location(s).
 

In GNU Emacs 24.0.50.1 (i386-mingw-nt5.1.2600)
 of 2011-09-19 on 3249CTO
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.5) --no-opt'