[9751] Add index by spell to character_spell

This is must fix porblem with long logins at
many broken spells in `character_spell` after client switch/etc.

sql/updates/9751_01_characters.sql

@@ -0,0 +1,3 @@
+ALTER TABLE character_db_version CHANGE COLUMN required_9702_01_characters_item required_9751_01_characters bit;
+
+ALTER TABLE `character_spell` ADD KEY `Idx_spell` (`spell`);