Disamb:  Consider names too when determining date disambiguations.

Previously if you had two distinct names needing disambiguation for
the same date, the letters would not start over with 'a' for the second
name.  Test case (from Nick Bart):

```
@item1, @item2, @item3, @item4

---
references:
- title: Title one
  id: item1
  issued:
    year: 2003
  author:
    given:
    - Al
    family: Author
  type: article-journal
  language: en-US
- title: Title two
  id: item2
  issued:
    year: 2003
  author:
    given:
    - Al
    family: Author
  type: article-journal
  language: en-US
- title: Title three
  id: item3
  issued:
    year: 2003
  author:
    given:
    - Al
    family: Buthor
  type: article-journal
  language: en-US
- title: Title four
  id: item4
  issued:
    year: 2003
  author:
    given:
    - Al
    family: Buthor
  type: article-journal
  language: en-US
...
```