New option "set debug symfile on".
	* NEWS: Mention "set debug symfile".
	* Makefile.in (SFILES): Add symfile-debug.c.
	(COMMON_OBS): Add symfile-debug.o.
	* elfread.c (elf_symfile_read): Use objfile_set_sym_fns to set the
	objfile's symbol functions.
	* objfiles.h (objfile_set_sym_fns): Declare.
	* symfile-debug.c: New file.
	* symfile.c (syms_from_objfile_1): Use objfile_set_sym_fns to set the
	objfile's symbol functions.
	(reread_symbols): Ditto.