* 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.
