gdb/

gdb/
	Code cleanup.
	* dwarf2read.c (dw2_map_symbol_filenames): Use symbol_filename_ftype
	for fun.
	* psymtab.c (map_symbol_filenames_psymtab)
	(map_partial_symbol_filenames): Likewise.
	* psymtab.h: Include symfile.h.
	(map_partial_symbol_filenames): Use symbol_filename_ftype for fun.
	* symfile.h (symbol_filename_ftype): New.
	(struct quick_symbol_functions): Use symbol_filename_ftype for fun of
	map_symbol_filenames, clarify more the naming in comment.