Fixed bug lp:826377 "Aria DB Format: Reading specific table from dump causes Wrong bytesec"

The bug was that when using bulk insert combined with lock table, we intitalized the io cache with the wrong file position.
This fixed a bug where MariaDB could not read in a table dump done with mysqldump.


mysql-test/suite/maria/r/locking.result:
  Test case for locking + write cache bug
mysql-test/suite/maria/t/locking.test:
  Test case for locking + write cache bug
storage/maria/ma_extra.c:
  Initialize write cache used with bulk insert to correct file length.
  (The old code didn't work if one was using LOCK TABLE for the given table).