fixed has_alt_urls? and has_redirect_to_url? conditions.

!alt_urls(page_or_post).empty? && !alt_urls(page_or_post).nil? were redundant conditions whenever value of page_or_post.data['redirect_from'] == nil. In this case alt_urls = [nil]
!alt_urls(page_or_post).nil?  was redundant because final output of alt_urls is always an array

Also, I think redirect_to_url should return a single url and not an array, in this way the name would make more sense. I you agree than I could make the necessary changes in the code and resubmit the pull request.