illumos gate

Analysis by George Wilson:

Running zdb after a ztest failure caused zdb to segmentation fault:

> $c
libzpool.so.1`spa_history_log_internal+0x47(888e000, fed8f6d0, 0, fed937a8, 0,
0
)
libzpool.so.1`spa_history_log_version+0x63(888e000, fed8f6d0, 1, fed1e77a)
libzpool.so.1`spa_import+0x102(87a8920, 87a8928, 0, 1, 0, 82ce89c)
main+0x4e8(1, 8047bf0, 8047c0c, 8047bac)
_start+0x7d(6, 8047ccc, 8047cd0, 8047cd3, 8047ce0, 8047ce3)

This happens to be a verbatim import so it ends up going through this code
path:

        /*
         * Verbatim import - Take a pool and insert it into the namespace
         * as if it had been loaded at boot.
         */
        if (spa->spa_import_flags & ZFS_IMPORT_VERBATIM) {
                if (props != NULL)
                        spa_configfile_set(spa, props, B_FALSE);

                spa_config_sync(spa, B_FALSE, B_TRUE);

                mutex_exit(&spa_namespace_lock);
                spa_history_log_version(spa, "import");

                return (0);
        }

The problem is that calling spa_history_log_version() will try to access the
dsl_pool_t which has not been opened yet.

Since verbatim imports are equivalent to a pool open we can simply remove the
call to spa_history_log_version() and allow it to get called in the open code
path.