actually use statusbar_pww in the statusbar prompt code to cut down on

actually use statusbar_pww in the statusbar prompt code to cut down on
redundant updates, add related functions to do that, and rename a few of
the statusbar prompt functions for consistency

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@3099 35c25a1d-7b9e-4130-9fde-d3aeb78583b8