vanilla version of Markus Kuhn's wcwidth.c plus wrapper code

wcwidth() function required to give column widths for UTF-8
and is required from solving remaining parts of STR-2158



git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@7529 ea41ed52-d2ee-0310-a9c1-e6b18d33e121