* arm-tdep.c (arm_frame_chain_valid): Remove unnecessary test.

	* arm-tdep.c (arm_frame_chain_valid):  Remove unnecessary test.
	* d10v-tdep.c (d10v_frame_chain_valid): Remove unnecessary tests.
	* hppa-tdep.c (hppa_frame_chain_valid): Remove unnecessary test.

	* blockframe.c: Include "gdbcmd.h" and "command.h".
	(backtrace_below_main): New variable.
	(file_frame_chain_valid, func_frame_chain_valid)
	(nonnull_frame_chain_valid, generic_file_frame_chain_valid)
	(generic_func_frame_chain_valid): Remove functions.
	(frame_chain_valid, do_flush_frames_sfunc): New functions.
	(_initialize_blockframe): New function.
	* Makefile.in (blockframe.o): Update dependencies.
	* frame.c (frame_saved_regs_id_unwind, get_prev_frame): Remove FIXME
	comment.  Call frame_chain_valid ().
	* frame.h: Remove old prototypes.  Add prototype for
	frame_chain_valid and update comments to match.
	* gdbarch.sh: Change FRAME_CHAIN_VALID into a predicated function.
	Remove old comment.
	* gdbarch.h: Regenerated.
	* gdbarch.c: Regenerated.

Plus updates to all other targets not to provide a FRAME_CHAIN_VALID.