Format latitudes and longitudes as %7f in XML output

[gravitystorm]

This matches the double formatting in XML from cgimap. Fixes #341.

[tomhughes]

There are test failures where things are selecting on the XML output:

  1) Failure:
ApiControllerTest#test_map_inclusive [/home/tom/src/osm/rails/test/controllers/api_controller_test.rb:92]:
Expected exactly 1 element matching "node[id='3'][lat='3.0'][lon='3.0'][version='1'][changeset='2'][visible='true'][timestamp='2007-01-01T00:00:00Z']", found 0..
Expected: 1
  Actual: 0


  2) Failure:
ApiControllerTest#test_map [/home/tom/src/osm/rails/test/controllers/api_controller_test.rb:70]:
Expected exactly 1 element matching "node[id='3'][lat='3.0'][lon='3.0'][version='1'][changeset='2'][visible='true'][timestamp='2007-01-01T00:00:00Z']", found 0..
Expected: 1
  Actual: 0


  3) Failure:
WayControllerTest#test_full [/home/tom/src/osm/rails/test/controllers/way_controller_test.rb:77]:
Expected exactly 1 element matching "osm node[id='3'][version='1'][lat='3.0'][lon='3.0']", found 0..
Expected: 1
  Actual: 0