Add also missing <stdlib.h> where required.

The generally recommended way is to include it from source files, not
headers. We had a mix of both. Let's try to be consistent and follow the
recommended way.

Runtime sellection of ARGB  XImage byte order

Our XRender code assumes a certain pixel layout which was not
guaranteed on big endian systems. The previous workaround only worked
for some cases, so fix this properly now.

Some platforms draw directly to the screen, which means that updates
will flicker if we draw multiple layers. Prevent this by first
composing the update on a hidden surface.

This will allow us to render more things than just the framebuffer.