Added unit tests for GraphId. Found and fixed issue with less than operator.

                 TestCtorDefault  [PASS]
            TestCtorUintUintUint  [PASS]
                    TestCtorCopy  [PASS]
                  TestGet_tileid  [PASS]
                   TestGet_level  [PASS]
                      TestGet_id  [PASS]
             TestSetUintUintUint  [PASS]
             TestOpPostIncrement  [PASS]
                  TestOpLessThan  [PASS]
                   TestOpEqualTo  [PASS]
Merge branch 'master' of https://github.com/mapzen/valhalla into gdg
Merge pull request #57 from mapzen/gdg

Added unit tests for GraphId. Found and fixed issue with less than operator.