* symfile.h (struct sym_fns) <next>: Remove.

	* symfile.h (struct sym_fns) <next>: Remove.
	(add_symtab_fns): Update.
	* symfile.c (sym_fns_ptr): New typedef.
	(symtab_fns): Now a VEC.
	(add_symtab_fns): Update.  Change argument type.
	(find_sym_fns): Update.  Change return type.
	(get_symfile_segment_data): Update.
	* objfiles.h (struct objfile) <sf>: Now const.
	* somread.c (som_sym_fns): Now const.  Update.
	* xcoffread.c (xcoff_sym_fns): Now const.  Update.
	* mipsread.c (ecoff_sym_fns): Now const.  Update.
	* machoread.c (macho_sym_fns): Now const.  Update.
	* elfread.c (elf_sym_fns): Now const.  Update.
	(elf_sym_fns_gdb_index): Likewise.
	* dbxread.c (aout_sym_fns): Now const.  Update.
	* coffread.c (coff_sym_fns): Now const.  Update.