Avoid max key length error in civicrm_option_value table.

civicrm.mysql.diff

--- civicrm.mysql.old	2013-03-19 22:28:40.000000000 +1300
+++ civicrm.mysql	2013-03-19 22:29:13.000000000 +1300
@@ -2531,20 +2531,10 @@
      `is_active` tinyint   DEFAULT 1 COMMENT 'Is this option active?',
      `component_id` int unsigned    COMMENT 'Component that this option value belongs/caters to.',
      `domain_id` int unsigned    COMMENT 'Which Domain is this option value for',
-     `visibility_id` int unsigned   DEFAULT NULL  
-,
-    PRIMARY KEY ( `id` )
- 
-    ,     INDEX `index_option_group_id_value`(
-        `value`
-      , `option_group_id`
-  )
-  ,     INDEX `index_option_group_id_name`(
-        `option_group_id`
-      , `name`
-  )
-  
-,      
+     `visibility_id` int unsigned   DEFAULT NULL,
+      PRIMARY KEY ( `id` ),     
+      INDEX `index_option_group_id_value`(value(200), option_group_id),
+      INDEX `index_option_group_id_name`(option_group_id, name(200)),      
      CONSTRAINT FK_civicrm_option_value_option_group_id FOREIGN KEY (`option_group_id`) REFERENCES `civicrm_option_group`(`id`) ON DELETE CASCADE,      
      CONSTRAINT FK_civicrm_option_value_component_id FOREIGN KEY (`component_id`) REFERENCES `civicrm_component`(`id`) ,      
      CONSTRAINT FK_civicrm_option_value_domain_id FOREIGN KEY (`domain_id`) REFERENCES `civicrm_domain`(`id`)