Separate core functions along target vector in preparation for

    Separate core functions along target vector in preparation for
        native support.  Functions above vector now live in core.c.  Those
        below in corelow.c.

	* core.c (solib_add_stub, core_close, core_open, core_detach,
	  get_core_registers, core_files_info, core_ops): moved to corelow.c
	  (_initialize_core): removed addition of core_ops target.
	* corelow.c: new file.
	(solib_add_stub, core_close, core_open, core_detach,
	get_core_registers, core_files_info, core_ops): moved from core.c
	(_initialize_corelow): new function.
	* gdbcore.h (core_open, core_detach): added prototypes.
	(core_ops): add forward declaration.
	* Makefile.in (SFILES_MAINDIR): add core.c
	(OBS): add core.o
	(TSOBS): change core.o to corelow.o