The system command, executes a command in a subshell under Unix or Windows.
# execute 'command' system command
cmd.system(string command,int async=0)
async can only be specified from the Python level (not the command language)
- if async is 0 (default), then the result code from "system" is returned in r
- if async is 1, then the command is run in a separate thread whose object is returned