Fix is done by doing an autocommit in truncate table inside Aria

storage/maria/ha_maria.cc:
  Force a commit for TRUNCATE TABLE inside lock tables
  Check that we don't call TRUNCATE with concurrent inserts going on.
  Make ha_maria::implict_commit faster when we don't have Aria tables in the transaction.
  (Most of the patch is just re-indentation because I removed an if level)