busybox

Hiroshi found another bug.  Currently sed's $ triggers at end of every file,
and with multiple files SuSv3 says it should only trigger at the end of the
LAST file.

The trivial fix I tried first broke if the last file is empty.  Fixing this
properly required restructuring things to create a file list (actually a
FILE * list), and then processing it all in one go.  (There's probably a
smaller way to do this, merging with append_list perhaps.  But let's get
the behavior correct first.)

Note that editing files in place (-i) needs the _old_ behavior, with $
triggering at the end of each file.

Here's a test of all the things this patch fixed.  gnu and busybox seds produce
the same results with this patch, and different without it.

echo -n -e "1one\n1two\n1three" > ../test1
echo -n > ../test2
echo -e "3one\n3two\n3three" > ../test3
sed -n "$ p" ../test1 ../test2 ../test3
sed -n "$ p" ../test1 ../test2
sed -i -n "$ p" ../test1 ../test2 ../test3