Map Categories: remember last number of categories chosen

```
In 1.4.3, when choosing a Quantile map, and specifying 6 categories (for
example), the number of categories in any other variable # category should
default to 6. Currently, it always defaults back to 4.
```

Original issue reported on code.google.com by `mmcc...@gmail.com` on 9 Sep 2013 at 8:30

Start at the Quantile map category selector and trace how the chosen category count is initialized when another variable is selected. Confirm that choosing a number such as 6 preserves that count for subsequent variable selections instead of resetting to 4.

Written by the indexing model from the issue text.