Added the checkown applet based on the work by Renato Caldas, #192682

checkdir ensures that the specified files (or directories) are owned
by the current user/group or as specified on the command line. You can
optionally check permissions too.

src/builtins.h

@@ -7,6 +7,7 @@
  * Released under the GPLv2
  */
 
+int checkown (int argc, char **argv);
 int env_update (int argc, char **argv);
 int fstabinfo (int argc, char **argv);
 int mountinfo (int argc, char **argv);