Remove duplicate casedn_str() in mysql_change_db()
Fix for null handling in CASE


innobase/btr/btr0sea.c:
  Auto merged
mysql-test/t/case.test:
  Auto merged
sql/ha_innodb.cc:
  Auto merged
sql/item_cmpfunc.cc:
  Auto merged
mysql-test/r/case.result:
  merge with 3.23
sql/sql_db.cc:
  Merge with 3.23 (to remove duplicate casedn_str())