Lock individual records in the timestamp file instead of the entire

file.  This will make it possible for multiple sudo processes using
the same tty to serialize their timestamp lookups.

include/sudo_util.h

@@ -182,6 +182,8 @@ __dso_public char *sudo_new_key_val_v1(const char *key, const char *value);
 #define SUDO_UNLOCK	4		/* unlock a file */
 __dso_public bool sudo_lock_file_v1(int fd, int action);
 #define sudo_lock_file(_a, _b) sudo_lock_file_v1((_a), (_b))
+__dso_public bool sudo_lock_region_v1(int fd, int action, off_t len);
+#define sudo_lock_region(_a, _b, _c) sudo_lock_region_v1((_a), (_b), (_c))
 
 /* parseln.c */
 __dso_public ssize_t sudo_parseln_v1(char **buf, size_t *bufsize, unsigned int *lineno, FILE *fp);