The bug was that prepared statements didn't downgrade TL_WRITE_CONCURRENT properly

mysql-test/r/maria.result:
  Added test case
mysql-test/t/maria.test:
  Added test case
sql/mysql_priv.h:
  Make upgrade_lock_type() global
sql/sql_base.cc:
  Fixed indentation
sql/sql_insert.cc:
  Make upgrade_lock_type() global
sql/sql_prepare.cc:
  Call upgrade_lock_type_for_insert() to get right lock to use
sql/sql_view.cc:
  Indentation fix