Seperate glX from HAVE_OPENGL, for platforms that have both an X server and a more official way to do OpenGL, explicitly check for glX on Mac OS X, and use SDL_LoadObject for platforms that have glX but don't have dlopen().

## Makefile.am for SDL using the iPod framebuffer driver

noinst_LTLIBRARIES = libvideo_ipod.la
libvideo_ipod_la_SOURCES = SDL_ipodvideo.c SDL_ipodvideo.h