This means that when using SDL 1.2 we use SDL_net 1.2, but when
using SDL 2 we now use SLD_net 2 as well. Both versions work
properly and there is not code change needed in ScummVM.
This change is because SDL_net depends on SDL, and using
SDL_net 1.2 with SDL 2 means we can end up needing to link with
both the SDL and SDL2 libraries.
Now Client reads the first headers block, then LocalWebserver decides
which Handler to use. In case of "/upload", UploadFileHandler is used.
But now it only knows the "path" parameter. If that's valid, actual
UploadFileClientHandler is created, which reads the contents of the
request and, when finds there an "upload_file" field, starts saving it
in the directory specified by "path".
With that we don't need temp files approach from Reader class.
That ClientHandler is made for responding GET requests. It calculates
stream's length, it allows to specify response code and headers, it can
be used to transfer any ReadStream.
