1 USERON
 This command tests to see if a user is logged on to the system.  The
 result can be displayed on the console or placed in a local symbol.

 Calling sequence:

        $ USERON :== $SYS$COM:USERON
        $ USERON user[ symbol]

 If no 'symbol' is given the result is displayed on the console.

 If the specified user is on the system 'YES' will be returned,
 otherwise 'NO' will be returned.

2 arguments
 The format of the two arguments are given below:

        user            1-15 character user name.

        symbol          1-255 character local symbol name.
