FUNCTION NKEY()

  Short:
  ------
  NKEY() Gets key of an index file

  Returns:
  --------
  <cKey> => index key expression

  Syntax:
  -------
  NKEY(cIndex)

  Description:
  ------------
  Gets key expression of index <cIndex>. <cIndex> is
  the name of the index including extension. The function operates
  differently from .ntx to .ndx.

  Examples:
  ---------
   for i = 1 to nIndexes

       ?"Key for index: "+aInd[i]+" is "+NKEY(aInd[i])

   next

  Warnings:
  ----------
  Uses up a file handle temporarily. Opens up the index
  with low level file functions.

  Notes:
  -------
  NKEY() expects the full path of the index file and if
  no path is passed, will use SET DEFAULT setting

  Source:
  -------
  S_NKEY.PRG