Get the date of a DBF last change.
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 Syntax

        GT_LUpDate(<cFileName>) --> dModification

 Arguments:

      <cFileName> is the name of the DBF file. If the name has no
      extension it defaults to DBF.

 Returns:

      The date that the DBF file was last changed.

 Description:

      GT_LUpDate() is designed to be the same as the Clipper function
      LUpDate(). The main change is that it works on un-opened database
      files.

 Examples:

      // Print the date that a DBF file was changed.

      ? GT_LUpDate("Life")

 Source: LUPDATE.PRG

 Author:  Dave Pearson