fix failing migration on mysql

We didn't specify that the db user needs the right to create
temporary tables before.
That's why the migration will fail on most installations.
This commits removes the "TEMPORARY" from the migration
and changes the documentation to include the necessary rights for the future.

db/migrate/20150817163600_deduplicate_user_identities.rb

 class DeduplicateUserIdentities < ActiveRecord::Migration
   def change
     execute 'DROP TABLE IF EXISTS tt_migration_DeduplicateUserIdentities;'
-    execute 'CREATE TEMPORARY TABLE tt_migration_DeduplicateUserIdentities AS SELECT id,provider,user_id FROM identities;'
+    execute 'CREATE TABLE tt_migration_DeduplicateUserIdentities AS SELECT id,provider,user_id FROM identities;'
     execute 'DELETE FROM identities WHERE id NOT IN ( SELECT MIN(id) FROM tt_migration_DeduplicateUserIdentities GROUP BY user_id, provider);'
     execute 'DROP TABLE IF EXISTS tt_migration_DeduplicateUserIdentities;'
   end

doc/install/database_mysql.md

@@ -36,7 +36,7 @@ We do not recommend using MySQL due to various issues. For example, case [(in)se
     mysql> CREATE DATABASE IF NOT EXISTS `gitlabhq_production` DEFAULT CHARACTER SET `utf8` COLLATE `utf8_unicode_ci`;
 
     # Grant the GitLab user necessary permissions on the database
-    mysql> GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, INDEX, ALTER, LOCK TABLES ON `gitlabhq_production`.* TO 'git'@'localhost';
+    mysql> GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, CREATE TEMPORARY TABLES, DROP, INDEX, ALTER, LOCK TABLES ON `gitlabhq_production`.* TO 'git'@'localhost';
 
     # Quit the database session
     mysql> \q