mysql-test/r/sp-threads.result:
  Testcase for BUG#12228
mysql-test/t/sp-threads.test:
  Testcase for BUG#12228
sql/sp_cache.cc:
  BUG#12228: Post-review fixes: small code cleanup
sql/sp_cache.h:
  BUG#12228: Post-review fixes: fixed the comment
sql/sql_parse.cc:
  BUG#12228: Post-review fixes: in mysql_parse, flush obsolete SPs from the caches only if 
   the query hasn't been handled by the query cache.
sql/sql_prepare.cc:
  BUG#12228: Post-review fixes: in mysql_stmt_prepare/execute, flush SP caches 
   "closer to the execution"