`wcwidth-upgrade': upgrade to latest wcwidth.c from Markus Kuhn

`wcwidth-upgrade': upgrade to latest wcwidth.c from Markus Kuhn
<http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c>.
This is identified both internally and in HTTP headers as 2003-05-20,
for Unicode 4.0.

Only changes from upstream are to make mk_wcwidth_cjk() non-static and to
#include "putty.h" for prototypes.

The status of some code points has changed; see the wishlist item. We've
had some feedback from the CJK and Arabic communities that upgrading is
probably the right thing to do.

git-svn-id: svn://svn.tartarus.org/sgt/putty@5547 cda61777-01e9-0310-a592-d414129be87e