* fileio.c: Fix some integer overflow issues.

* fileio.c: Fix some integer overflow issues.

(file_name_as_directory, Fexpand_file_name, Fsubstitute_in_file_name):
Don't assume string length fits in int.
(directory_file_name): Don't assume string length fits in long.
(make_temp_name): Don't assume pid fits in int, or that its print
length is less than 20.