term: handle fullwidth chars in the last column

term: handle fullwidth chars in the last column

This handles wrapping double-width characters when inserted in the
last column of the screen.  Felix Janda <felix.janda@posteo.de>
reported this case and prepared a preliminary patch.

Handling fullwidth characters was originally suggested by Sara Fauzia
<sfauzia@fas.harvard.edu> which resulted in a simple patch to simply
ignore these characters in the bold branch.  A recent request and
patch from Felix Janda <felix.janda@posteo.de> motivated me to apply a
modified version to the master branch.