sys_vswprintf relies on platform-specific printf implementations, which
vary widely between platforms (in handling of truncation, return values,
use of %s/%S/%hs/%ls for mixing char and wchar_t strings, etc) and are
therefore a pain.
Use cppformat's fmt::sprintf instead, which has very similar syntax to
sprintf but is more C++ish and is portable.
Also, wchar_t is stupid, so use char* strings (which are expected to be
UTF-8) in CLogger. This creates a bit of a pain with changing all
callers to convert to char* strings, but that's their fault for not
using UTF-8 already.
Refs #3011.
This was SVN commit r16182.
leper