Dbf:AddNtx(cName,cFile,cKey,lUnique): public: return true
  Last new created object OneDbf is appended with definition of next index
  file.

  Parameter description:
  ~~~~~~~~~~~~~~~~~~~~~~
  cName: character: no default
   Menu item name for selection of this index file (SET ORDER).

  cFile: character: no default
   Index file name.

  cKey: character: no default
   Key expresion for index file.

  lUnique: logical: default is false
   Controls the UNIQUE index keys.