fixed e and x options in watch

fixed e and x options in watch

The -e option would print a confusing error message. This is because
most error messages in watch are one word.  This fix makes a more
sensible message about what went wrong.

The -x option exited before the endwin() function was called, so if the
child process died the terminal was left in a funky state. endwin is now
called just before the exit(8) for the -x option.