Validate a time string
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 Syntax

        H_ValidTime( cTime )

 Arguments:

      cTime - Time string to be validated

 Returns:

      .T. if string is valid
      .F. otherwise

 Description:

      Checks that the string is a valid time in the format hh:mm:ss

 Examples:



 Source: TIMEVALI.PRG

 Author:  Nantucket