_mailboxes and mutt backticks

[Clint Adams <schizo@debian.org>]

In the muttrc, one may use backticks in the 'mailboxes' specification.
On init, mutt passes each string enclosed in backticks to 'sh -c',
and expands the result.

Currently, zsh's _mailboxes does not cope with this.  I applied the
patch below, which does not seem to be an ideal solution.

Also, with or without this patch, and with or without backticks in
my muttrc, my first completion from mutt -f <TAB> is /, which is
not very useful at all.  This does not happen under a vanilla compinit
from zsh -f but I haven't tracked down which style or option is relevant.

--- /usr/share/zsh/functions/_mailboxes	Sun Oct 22 01:52:12 2000
+++ _mailboxes	Sun Nov  5 09:10:06 2000
@@ -62,15 +62,15 @@
 _mailbox_cache () {
   # Depends on $maildirectory and $pinedirectory from _mailboxes!
 
-  local i j muttrc="${muttrc:-~/.muttrc}"
+  local i j _mc_tmp muttrc="${muttrc:-~/.muttrc}"
   local -aU dirboxes
   typeset -aU -g _mailbox_cache
   typeset -aU -g _maildir_cache _mbox_cache _mh_cache _mutt_cache _pine_cache
 
 
   [[ -f ${~muttrc:-.} ]] &&
-    _mutt_cache=( ${=${(M)${(f)"$(<${~muttrc})"}:#mailboxes *}#mailboxes *} )
-
+    _mc_tmp=${=${(M)${(f)"$(<${~muttrc})"}:#mailboxes *}#mailboxes *} &&
+    _mutt_cache=( ${=${(Xe)_mc_tmp}} )
 
   _mbox_cache=( ${~maildirectory}/*(^/) )
   _pine_cache=( ${~pinedirectory}/**/*(.) )