Change the current directory.
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 Syntax

        GT_ChDir(<cDir>,[@<nError>]) --> lChanged

 Arguments:

      <cDir> is the path of the directory.

      <nError> is an optional parameter that must be passed by reference.
      If the directory change fails the DOS error code will be placed in
      this variable.

 Returns:

      If the change was made, GT_ChDir() returns true (.T.), if not it
      returns false (.F.).

 Description:

      GT_ChDir() can be used to change the current directory.

 Examples:

      // Change directory.

      nError := 0
      if !GT_ChDir("Knight",@nError)
         ? "Error =",nError
      endif

 Source: CHDIR.C

 Author:  Dave Pearson