[VM] Non-ASCII IMAP folder names

[Konrad Hinsen]

I noticed that IMAP folder names containing non-ASCII characters are
represented incorrectly in VM. They work perfectly well, but the name
that is displayed (and required for input) is messed up. For the
German and French names I have in my account that's not so bad, but I
wouldn't want to deal with Greek or Chinese names.

I explored the issue a bit and found that the folder names are not
decoded from UTF-7 (which is what IMAP specifieds). The raw UTF-7
strings are used as Emacs strings. Inserting a simple utf7-decode
produces a perfectly fine folder list, but then all actions on those
folders fail because the folder names are not properly re-encoded in
UTF-7.

I stopped at that point because I don't have a good enough overview of
IMAP folder handling in VM to decide at what level UTF-7 encoding and
decoding should best be implemented. It's not a vital issue but still
something that should be on the to-do list.

Konrad.