add chdir option to makeflow

We define this option as 'X'. There are three places needed to be updated.
In main() function:
1. Add one item in static struct option long_options_run[] = {}
{"change_directory", required_argument, 0, 'X'},

2. Also add this 'X' in const char *option_string_run
const char *option_string_run = "aAB:cC................................X:zZ:";

3. Add the definition of option 'X' in switch statement.
 case 'X':
   chdir(optarg);
   break;

And the 'X' option will work as this: makeflow  -X  foo  Makeflow