merge

* harbour/contrib/rddads/adsx.c
    ! fixed adsSeek() if seek string length is less than index key length

  * harbour/src/compiler/hbopt.c
    ! improved BEGIN/END SEQUENCE support in code trace optimizer. Problem
      of false positive warning 'Variable is assigned but not used' is solved
      in cases like:
        FUNC TEST()
          LOCAL n := 1
          BEGIN SEQUENCE
            IF n == 1
              n := 2
              BREAK
            ENDIF
            n := 3
          END SEQUENCE
          RETURN n
    ; TODO: test for more complicated cases like nested BEGIN/END SEQUENCE

  * harbour/src/rdd/dbf1.c
    * added :GetValue() GPF protection if area is "half opened" (ex.,
      enumerating field values in error handler on area open failure).
      More general solution for "half opened" workareas is welcome