Relax precision of floating point comparison in test.
Relax precision of floating point comparison in test.

Comparing exactly equal was giving the error message below, which differs only in the 15th decimal place. This is a difference of a fraction of a micrometer, so I think we can call it "good enough". Sadly, there doesn't seem to be an `assertAlmostEqual` which recurses as `assertEqual` does, so the comparison needed to be expanded.

```
======================================================================
FAIL: test_convert_coord (tests.test_tile.TestCoordToBounds)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tilequeue/tests/test_tile.py", line 54, in test_convert_coord
    self.assertEqual(exp_bounds, bounds)
AssertionError: Tuples differ: (-74.00390625, 40.697299008636... != (-74.00390625, 40.697299008636...

First differing element 3:
40.713955826286046
40.71395582628604

- (-74.00390625, 40.69729900863674, -73.98193359375, 40.713955826286046)
?                                                                     -

+ (-74.00390625, 40.69729900863674, -73.98193359375, 40.71395582628604)

----------------------------------------------------------------------
```

mapzen/tilequeue,tilezen/tilequeue