In ha_innobase::create(), we check some things while holding an
exclusive lock on the data dictionary. Defer the locking and the
creation of transactions until after the checks have passed. The
THDVAR could hang due to a mutex wait (see Bug #11750569 - 41163:
deadlock in mysqld: LOCK_global_system_variables and LOCK_open), and
we want to avoid waiting while holding InnoDB mutexes.

innobase_index_name_is_reserved(): Replace the parameter trx_t with
THD, so that the test can be performed before starting an InnoDB
transaction. We only needed trx->mysql_thd.

ha_innobase::create(): Create transaction and lock the data dictionary
only after passing the basic tests.

create_table_def(): Move the IS_MAGIC_TABLE_AND_USER_DENIED_ACCESS
check to ha_innobase::create(). Assign to srv_lower_case_table_names
while holding dict_sys->mutex.

ha_innobase::delete_table(), ha_innobase::rename_table(),
innobase_rename_table(): Assign srv_lower_case_table_names as late as
possible. Here, the variable is not necessarily protected by
dict_sys->mutex.

ha_innobase::add_index(): Invoke innobase_index_name_is_reserved() and
innobase_check_index_keys() before allocating anything.

rb:618 approved by Jimmy Yang