bug #5001, added conditional if to test if port set, then only kill the processes
  for this port, not all processes (in the case of this bug where multiple servers 
  are killed.)
  The change to the 'grep' to make sure mysqld_safe isn't killed was per Serg's
  discovery that mysqld_safe would get killed. 
  In my testing, in killing one of the pids for a running server, the "if test ! -f $pid_file"
  was the case that evaluated as true, so in order to test, I had to comment that block
  out.