Get the header size of a DBF file.
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 Syntax

        GT_Header(<cFileName>) --> nHeaderSize

 Arguments:

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

 Returns:

      The size of the header in the DBF file.

 Description:

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

 Examples:

      // Print the header size of an un-opened database file.

      ? GT_Header("Life")

 Source: HEADER.PRG

 Author:  Dave Pearson