SEEK_END and SEEK_SET do not visible for mingw (there is no #include <stdio.h> in the include tree for SDLpp/RWops.cc).
Both constants are using for RWops::Seek -> SDL_RWseek, which accepts "whence" as one of defines RW_SEEK_SET/RW_SEEK_CUR/RW_SEEK_END.
My suggestion is: replace SEEK_END -> RW_SEEK_END, SEEK_SET -> RW_SEEK_SET.
Now it explicitely stores name of SDL function which caused an error
and generates complete user-readable error message which contains both
function name and SDL error message. Users can now handle SDL2pp
exceptions along with all others in `catch (std::exception&)' and
get complete error info.
While here, fixed incorrect function names in some throw's
