Stat cleanup.

Stat cleanup.

lib: rename format_mode() to mode_to_string() (echoing string_to_mode), make it
take a normal char * argument.

stat: collapse big switch/case statements that only have one line each
into if/else staircase (much fewer lines of code). Remove return type
(other stat implementations print ? for unknown escapes, so do that here).
Inline do_stat() and do_statfs(). Set default string in normal local
variable "format". Remove unnecessary struct d. Restructure stat logic to
"if (flagf && !statfs()) else if (!flagf && !stat()) else perror_msg();"
Teach %N to add -> symlink. Judicious use of putchar() instead of xputc to
let FILE * do its job collating output.