Fix compilation errors.

Demo should now compile on Linux and FreeBSD.
remove USE_CG for now

This used to trigger the runtime assembly that was driving the 8bit
cpu. On today's machines it's hardly relevant. It requires also the
ccg assembler and some other source files.
remove xdnd

drag'n'drop was not used in +1-1 and was a remnant of some unreleased
projects.
rename macosx_main_loop into default_main_loop

it does not use any macos-isms and works on unix like platforms.
Merge branch 'F-FixUnixCompilation'

* F-FixUnixCompilation:
  rename macosx_main_loop into default_main_loop
  remove xdnd
  remove USE_CG for now
  Fix compilation errors.