Change the unifont API so that text is passed right down to the

Change the unifont API so that text is passed right down to the
individual font implementation as wchar_t, rather than having to be
converted by the client into the appropriate MBCS/SBCS.

This also means I can remove 'real_charset' from the public-facing
contents of the unifont structure.

git-svn-id: http://svn.tartarus.org/sgt/putty@9292 cda61777-01e9-0310-a592-d414129be87e