bug#6721: X11 Compound Text vs ISO 2022

[David De La Harpe Golden <david@harpegolden.net>]

Logging issue to tracker so it doesn't disappear behind certain recent 
mammoth junk threads:

James Cloos raised on emacs-devel:
http://lists.gnu.org/archive/html/emacs-devel/2010-07/msg00255.html

The problem that emacs has been sending "compound-text" using charsets 
not generally supported by other X11 clients.   The spec for compound 
text seems clear enough, emacs shouldn't do that (though maybe should 
remain permissive in what it accepts).

Emacs has compound-text and compound-text-with-extensions, the latter 
having support for some widely used extensions to the original spec
including embedded unicode.

Compound-text-with-extensions (since it supports embedded unicode) and 
probably compound-text should be restricted to only encoding to the 
known shortlist of acceptable charsets for compound-text, including some 
but not all of the iso2022 charsets emacs presently supports.

Given UTF8_STRING support in X11, I reckon it is fairly unlikely the set 
of acceptable compound text charsets will be expanding much in future.

Emacs should also probably use compound-text-with-extensions in the 
places it is currently using compound-text (or just make the former its 
latter)