Start working on improving UTF-8 support.

This change adds support for 16+bit unicode. This started from a
reading of http://www.cl.cam.ac.uk/~mgk25/ucs/utf-8-history.txt, and
taking help from some code there. There are some issues regarding
refreshing the screen contents, and the copy/search functions need
to be updated, but this is a good first step.
Fix screen refresh issues.

Some fix in pointer arithmetic seems to have fixed the screen
refresh issues. Also, remove some comments.
Fix copying and searching for 16+bit unicode.
Encode before dumping.

Do the necessary encoding before dumping hardcopy/scrollback into a
file.
Do not go over the array bound.
Fix encoding into 16+bit unicode.

This fix to 16+bit unicode encoding should fix hardcopy/log issues.
Remove compile warnings.
Fix refresh when double-cell characters end a line

Double cell characters that end a line are not properly displayed
when there are split regions. Takeshi Banse detected the problem and
a fix for it in Savannag bug #29106. This is a better fix, as it
will catch some more cases of the same problem. But this particular
fix is usable only with the changes made for better unicode support
in unicode++ branch.
Changelog.
Fix autoaka.
Merge branch 'master' into unicode++
Doc addenum to command displays.

Closes savannah #29374.
Merge branch 'master' into unicode++
Merge remote-tracking branch 'origin/master' into unicode++
Merge branch 'unicode++' of git://git.savannah.gnu.org/screen into shyouhei/term-max