crsmithdev/arrow — pull request #164 by zakhar (2014-09-12 12:37:22+00:00)
Title: fix span_range for week frame

I found the problem in `span_range` function related to week frame.

```
In [5]: arrow.Arrow.span_range('week', arrow.Arrow(2014, 9, 10), arrow.Arrow(2014, 9, 16))
Out[5]:
[(,
)]
```
but if I shift start_date early, I get the extra week:
```
In [6]: arrow.Arrow.span_range('week', arrow.Arrow(2014, 9, 9), arrow.Arrow(2014, 9, 16))
Out[6]:
[(,
),
(,
)]
```
The second behavior, I think, correct: all tests of other time frames include period with end date. So I correct the `span_range` test for week (add absent period) and fix the behavior of `span_range` to pass it.