Added way tests.
Added relation tests.
Added 'empty' test cases, which are really about Accept headers.
Added (experimental) node ways test cases.
Added way/full test cases.
Added relation/full test cases.
Fixed empty cases, wasn't using the right header.
Move start/end formatter calls to `osm_responder`.

Were in backends, but were simply duplicated in all backends. So
this reduces redundant code and also prevents errors - like the
one I made when I forgot to add the formatter start/end calls to
the static XML backend.
Added ability to test JSON document responses.
Translated JSON test case.
Changes to autotools for new tests, removing old tests.