Fix issue with pid://../run/foo..pid parser

Unfortunately we cannot use realpath(3) here since the the PID files
usually do not yet exist at this point.

Add and modify my ugly de_dotdot() from Merecat httpd.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/util.h

@@ -72,6 +72,7 @@ char *uptime       (long secs, char *buf, size_t len);
 char *memsz        (uint64_t sz, char *buf, size_t len);
 
 char *sanitize     (char *arg, size_t len);
+void  de_dotdot    (char *file);
 
 int   ismnt        (char *file, char *dir, char *mode);
 int   fismnt       (char *dir);