Drop SDL 1.3 fixes in preparation for SDL 2.0 support.
Initial SDL2 port. Backwards compat is broken. Software only.
Add a workaround to allow SDL initialization without joystick support.

SDL 2.0 doesn't build against the Windows 8.1 WDK because
DirectInput/COM/xinput support seems to be missing. My
build therefore does not include joystick support.

First try to init with joystick support, and then fall back
to going without if it doesn't work.
More fixes for more recent snapshot of SDL 2.0.
Fix up OpenGL renderers.
Make gp2x renderer compile. Doesn't quite work yet.
Add a way to test the gp2x renderer with SDL 2.0.

SDL 2.0's window pixel format is now 'take it or leave it', you
can't specify a the required format. Because the GP2X renderer
renders in 8bpp, then upmixes when scaling to 16-bit (the
format of choice on GP2X, presumably), we need to guarantee
16-bit output.

Add such support by allocating a shadow 16-bit framebuffer. The
renderer upmixes into this shadow, then the shadow is blitted
by SDL into the real window. This only happens if the real window
isn't already 16-bit.
Move gp2x blit workaround into generic path.

Also allow 32-bit software rendering to work with alpha surfaces
by OR'ing 0xFF into the XOR'ed mouse cursor rendering.
Fix up X clipboard support, partially.
Fix up mouse warping.
Restore window caption and icon support.
Fix a fixme.
Move SDL 1.2 compatibility helpers into compat.h.
Update deps package with SDL2 binary build.
Restore backwards compatibility with SDL 1.2.
CONFIG_X11 build fix.
Emulate SDL 1.2's 'unicode' feature with SDL 2.0.