Add $change_folder_next option to control mailbox suggestion order.

Add $change_folder_next option to control mailbox suggestion order.

This patch is out of the Gentoo package maintained by Fabian Groffen.
From the link below, it appears the original author was Simon Burge.

I made some minor changes to get it to apply correctly, and cleaned up
the documentation a bit.

Original patch description:
This patch brings back the original behaviour of change-folder, which
some people find more useful.  It suggests the next folder in your
mailboxes list that has new mail measured from the current folder,
instead of the first folder from your mailboxes list in any case.  This
prevents starvation of folders defined at the back of your list ;)
See discussion: http://thread.gmane.org/gmane.mail.mutt.devel/12457