the data dictionary locked across the operations.

dict_table_decrement_handle_count(), row_prebuilt_free(): Add the flag
dict_locked, to prevent the acquisition of dict_sys->mutex.

innobase_rename_table(): Rename commit_flag to lock_and_commit,
and do not acquire dict_sys->mutex or flush the log unless the flag is set.
Remove bogus comment about utility threads, because the threads will
be waken up by the upper-level function ha_innobase::rename_table().

ha_innobase::add_index(): After creating a primary key, hold dict_sys->mutex
across all dictionary operations.