tidy_mappings dedupes on query_string
two-pass tidy mappings in munge

The first tidy_mappings de-dupes, using rules such as 301 overriding
a 410. The second pass trumps to resolve conflicts.
re-munged scotlandoffice
decc only has filepath in the query_string
Merge pull request #153 from rjc123/newmappings

New Mappings for DH and Home Office
Merge pull request #152 from rjc123/newsites

New mappings for upcoming departments
remunge decc
Merge branch 'master' of git://github.com/alphagov/redirector