Prints the given string to the screen and into a file.
Used by command scripts to log messages.

usage: logmsg.cmd < message | @filename > [logfile]

  /t           If specified, the message is timestamped.

  message      Specifies the text to be logged, should 
               be quoted. 

  filename     A filename preceeded by an at-sign (@)
               may be given instead of a message. The
               contents will be appened into the log 
               if the given file exists.

  logfile      Specifies the name of the log file.
               LOGFILE, if defined, is the default.
               If this parameter is not specified and 
               LOGFILE is not defined, the message is 
               displayed on the screen only.

ex: call logmsg.cmd "This is the message to display."
    call logmsg.cmd @mylog.txt