remove still more redundant screen updates; change all wrefresh() calls

remove still more redundant screen updates; change all wrefresh() calls
to wnoutrefresh() calls, except for those in total_update() and
do_credits(); call doupdate() just before using blocking input, since
nano spends the most time using it, for blocking input; and only do
constant sursor position display if we're just about to use blocking
input

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2943 35c25a1d-7b9e-4130-9fde-d3aeb78583b8