This patch is the second part of implementation for cursor's statement
re-parsing. The patch does the following changes:
  - implements placing of items in SP instruction's free_list when
    a statement of failing SP instruction is re-parsed. New items are allocated
    on mem_root of SP instruction
  - on re-parsing a failed SP instruction that does need to get access
    to LEX a new lex is instantiated for every SP instruction except cursor
    relating SP instructions.
  - items created on re-parsing a cursor relating statement are moved
    to the free_list of sp_lex_cursor.