log message to:
- only log the message if the "full command line" is different than the
  command-line argument to the external() function. I'm pretty sure that was
  the reason for the addition of this log message, for debugging Linux-DOSEMU
  issues where the fullcmdline != cmdline.
- change from INFO to DEBUG log level
- change the message from "executing external: " to "Executing cmd-line: "