Commented out several instances of drop-index that were dropping indexes that do not exist in all Roller databases and cause the migration script to fail. There does not seem to be a "drop index if exists" capability in MySQL.

Also added and commented out an additional drop-index call for a column that does exist in some Roller databases and will cause the bookmark folder migration to fail.

git-svn-id: https://svn.apache.org/repos/asf/roller/trunk@1612158 13f79535-47bb-0310-9956-ffa450edef68