gnus-search & imap: always "CHARSET UTF-8" when literal+ is supported

[David Edmondson]

Using current emacs git head, talking to outlook.office365.com over
IMAP.

Attempts to use gnus-search always fail with the server reporting:

(("NO" ("BADCHARSET" "(US-ASCII)") "The" "specified" "charset" "is" "not" 
"supported."))

Looking at gnus-search.el, `gnus-search-imap-search-command' always
sends CHARSET UTF-8 if the server supports literal+ (which this one
does). Sending US-ASCII (or no charset at all) causes the server to
return the required results in simple test cases.

Is there a way to determine whether a server supports UTF-8 in searches,
and adjust the command sent accordingly? If not, could the use of UTF-8
be controlled with (yet another!) variable?

Thanks.

dme.
-- 
You know, somebody somewhere owes us a favor.