1. Fix DBUG_ASSERT(!table->pos_in_locked_tables) in tc_release_table();
2. Fix access of prematurely freed MDL_ticket: don't close ticket if table was not closed;
3. Fix deadlock after erroneous ALTER.

mysql_alter_table() leaves dirty table->m_needs_reopen in case of
error exit which then incorrectly treated by mysql_lock_tables().