Reversing the bottom-up images in the server is not needed since Pixman,
in the client, is able to deal with them. As a result, the previous code
was more complex and wrong. This commit fixes and cleans it.
- Add lz4 encoder to compress an image of type LZ4 (see spice_common).
- Add code in red_worker to use LZ4 when it is enabled, and the client
supports it through its display capability, or fallback to LZ.
- Add enable_lz4 switch in the configure script. Show LZ4 support at the
end.