ZMail now handles mouse clicks more robustly in message editing mode.

If, while editing a message in the bottom (message text) window, a user
clicks any mouse button in the top (summary) window, the editing is
saved, :edit mode is exited, and Zmail jumps to the clicked-on message
line.

If, while editing, the user clicks on a menu command, ZMail warns the
user that menu commands are not executable from within :edit mode, and
then fquery's the user as to whether or not to exit :edit mode at that
time.  If the user responds with "Y", :edit mode is exited, all editing
to the message is saved in the body of the message, the user is
presented with a reminder to reclick to execute the particular menu
command, and the top level command loop is re-entered.

If the user responds with "N", then ZMail simply reminds you that the
<End> and the <Abort> keys may be used to exit an edit session when you
are finished with the text.