Remove now-inaccurate comment about the files

Remove now-inaccurate comment about the files
you need to include first.  You don't need to include any files
other than the usual config.h.
Include <inttypes.h> and <stdint.h> if available, for uintmax_t.
Remove 'struct stat;' not needed since we know sys/stat.h has
been included by dev-ino.h.
(struct cycle_check_state): Change chdir_counter to uintmax_t,
not size_t, since it isn't limited by object sizes.
Change magic from long unsigned int to int; that's good enough
for our use.