Find the workarea of an alias
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 Syntax

        GT_Alias(<cAlias>) -> nArea

 Arguments:

      <cAlias> is the alias to find.

 Returns:

      nArea

 Description:

      Find the workarea of an alias

 Examples:

      // Which area contains the invoices file ?
      nArea := GT_Alias('INVOICES')

 Source: GT_ALIAS.PRG

 Author:  Martin Bryant