The parameter --innodb-sync-debug, which is disabled by default,
aims to find potential deadlocks in InnoDB.

When the parameter is enabled, lots of tests failed. Most of these
failures were due to bogus diagnostics. But, as part of this fix,
we are also fixing a bug in error handling code and removing dead
code, and fixing cases where an uninitialized mutex was being
locked and unlocked.

dict_create_foreign_constraints_low(): Remove an extraneous
mutex_exit() call that could cause corruption in an error handling
path. Also, do not unnecessarily acquire dict_foreign_err_mutex.
Its only purpose is to control concurrent access to
dict_foreign_err_file.

row_ins_foreign_trx_print(): Replace a redundant condition with a
debug assertion.

srv_dict_tmpfile, srv_dict_tmpfile_mutex: Remove. The
temporary file is never being written to or read from.

log_free_check(): Allow SYNC_FTS_CACHE (fts_cache_t::lock)
to be held.

ha_innobase::inplace_alter_table(), row_merge_insert_index_tuples():
Assert that no unexpected latches are being held.

sync_latch_meta_init(): Properly initialize dict_operation_lock_key
at SYNC_DICT_OPERATION. dict_sys->mutex is SYNC_DICT, and
the now-removed SRV_DICT_TMPFILE was wrongly registered at
SYNC_DICT_OPERATION.

buf_block_init(): Correctly register buf_block_t::debug_latch.
It was previously misleadingly reported as LATCH_ID_DICT_FOREIGN_ERR.

latch_level_t: Correct the relative latching order of
SYNC_IBUF_PESS_INSERT_MUTEX,SYNC_INDEX_TREE and
SYNC_FILE_FORMAT_TAG,SYNC_DICT_OPERATION to avoid bogus failures.

row_drop_table_for_mysql(): Avoid accessing btr_defragment_mutex
if the defragmentation thread has not been started. This is the
case during fts_drop_orphaned_tables() in recv_recovery_rollback_active().

fil_space_destroy_crypt_data(): Avoid acquiring fil_crypt_threads_mutex
when it is uninitialized. We may have created crypt_data before the
mutex was created, and the mutex creation would be skipped if
InnoDB startup failed or --innodb-read-only was specified.