PATCH: Several enhancements to mailbox checking

["M . Thielker" <balsa t-data com>]

HI,

 this patch fixes a major annoyance and
a few minor issues in mailbox checking
and adds a few choices for the user.

When background mailbox checking is
enabled and the progress dialog is
enabled as well, the dialog will appear
every time the background check is done.
With this patch, the progress dialog is
used only when the mail check is
initiated by user action, the background
check always uses the task bar for
status display.

For those, like me, who don't want that
flickering in the status bar, that
display can now be turned off through
prefs, making the bacjground mail check
completely invisible. I run it every 2
minutes and the status display gets on
my nerves.

When IMAP servers are used for storage
of messages only, there is no need to
regularly check them for new mail. A new
option in prefs allows the user to
select if IMAP mailboxes should be
checked for new mail at all.

I have experienced UI hangs during the
background mail check, the "Quiet"
option may serve to work around those,
too. If so, the hangs may be caused by
by the UI rather than libmutt....

Still more code?? :)

Melanie