Update to support fast removal of fields from the database. Previously it would iterate through every page using a field and delete the data individually. This is necessary for fields like FieldtypeFile, but not necessary for most. So it's been updated to perform the same task in a single query without loading all the pages, when it can. If it's dealing with less than 200 pages, or if the Fieldtype defines a ___deletePageField method, then it continues to use the old/slow method, as I don't think there is any way around that. This commit also includes some changes working towards support of InnoDB.