Do not capitalize page titles when importing dump

Capitalization of titles led to duplicates in SQL key for namespace and title if a corresponding upper-case title was already contained in the dump. This is most probably also the source of the duplicate key problem mentioned in #221.

An excerpt from the German Wikipedia dump which triggers this error is available at: https://gist.github.com/dfleischhacker/5f883e45e9afba4e5ec4