Unicode support for wxString (wxchar.cpp won't compile without it, so I

Unicode support for wxString (wxchar.cpp won't compile without it, so I
figured I couldn't hold it back anyway).
Added many macros. Changed most char to wxChar, and literals wrapped in _T().
Added conversion classes. Added new constructors to wxString, and mb_str(),
wc_str(), and fn_str() (the last is mb_str() on Unix and c_str() on Windows,
since Windows takes file names in Unicode (I think), while Unix doesn't).
Rewrote wxString::Printf().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@2109 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775