chmod() override with symbolic and ls-style modes

 File::chmod is a utility that allows one to bypass system calls or bit
 processing of a file's permissions. It overloads the chmod() function with
 its own that gets an octal mode, a symbolic mode, or an "ls" mode. If you
 wish not to overload chmod(), you can export symchmod() and lschmod(),
 which take, respectively, a symbolic mode and an "ls" mode.