After trying multiple inheritance (to messy and hard make it work) and
  sublassing jump_if_not (worked, but ugly), decided to on this solution
  instead:
  Inserting an abstract sp_instr_opt_meta class as parent for all instructions
  with destinations makes it possible to handle a continuation pointer for
  sp_instr_set_case_expr too.
  Note: No special test case; the fix is captured by the changed behaviour of
  bug14643_2, and bug14498_4 (formerly disabled), in sp.test.


mysql-test/r/sp.result:
  Updated results for BUG#16568 (affects results for bug14643_2 and bug14498_4)
mysql-test/t/sp.test:
  Enabled test bug14498_4 for BUG#16568.
sql/sp_head.cc:
  Changed type of some parameters and variables (sp_instr_opt_meta instead of sp_instr_jump*).
  Added consistency check of m_ip member in instructions in sp_head::show_routine_code().
  Updated print() method of, and added opt_mark() and opt_move() methods to
  sp_instr_set_case_expr, to handle the new continuation destination.
sql/sp_head.h:
  New abstract class between sp_instr and instructions with destinations, in particular
  sp_instr_set_case_expr, for continuation destination handling.
  Changed type of some parameters and variables (sp_instr_opt_meta instead of sp_instr_jump*).
  Added opt_mark(), opt_move() and set_destination() methods to
  sp_instr_set_case_expr.
sql/sql_parse.cc:
  Fixed small bug at show_routine_code() call (tested return value the wrong way).
sql/sql_yacc.yy:
  sp_instr_set_case_expr is now added to backpatch list (for the new cont. destination).