* Remove JIT_RET and JIT_FRET. Only interface to these should
	be jit_retval, jit_retval_f and jit_retval_d, otherwise one
	may use JIT_RET and/or JIT_FRET as argument to other jit calls,
	what may cause problems at least on the arm backend.

	* Update documentation to match new implementation.

	* Make an sparc port to not remove previous functionality.

	* Test and correct the ppc and mips ports, after the import and
	adaptation of the code to lightning.