xmlsitemap 6.x-2.0-unstable2

Changes since DRUPAL-6--2-0-UNSTABLE1:

• #554282 by Dave Reid: Fixed index dropping before column dropping.
• by Dave Reid: Re-added the {xmlsitemap}.langauge column in preparation for language-aware sitemaps.
• by Dave Reid: Synced with local dev version.
• #480490 by Dave Reid: Added hook_xmlsitemap_query_alter() and a starting implementation on behalf of i18n.module.
• by Dave Reid: Followup for previous commit.
• by Dave Reid: Added missing files to files[] in xmlsitemap.info.
• by Dave Reid: Added 5000 as a batch limit option and enforced that the auto chunk size is the recommended option.
• by Dave Reid: Removed the error suppression for db_drop_index().
• by Dave Reid: Reverse the order of the priority options so it goes biggest to smallest. Seems more logical this way.
• by Dave Reid: Revert removing the _xmlsitemap_translation_strings() function.
• by Dave Reid: Switch a function_exists() to a module_exists().
• #518710, #518702 by Dave Reid: Customize priority and language of custom links.
• by Dave Reid: Followup to remove unnecessary code.
• #554746 by Dave Reid: Fixed a division by zero error from a stupid logic error.
• by Dave Reid: Cleaned up settings validation logic.
• #554876 by Dave Reid: Fixed error when booleans are passed in _xmlsitemap_check_changed_link() from xmlsitemap_save_link().