not storing both key and record

hey, so i'm having some trouble with inserts into the tree.

I run the following code:
```
var strata = new Strata({ directory: "./bt", leafSize: 1024, branchSize: 1024 });
strata.create((err,test) => {
strata.mutator("rdf/3/A", (err,cursor) => {
console.log(err);
cursor.insert("rdf/3/A", {data:"test2"}, ~cursor.index);
cursor.unlock(() => {
});
});
});
```

that all goes fine, but when i run:

```
strata.open((err,test) => {
strata.iterator("rdf/3/A", (err,cursor) => {
console.log(cursor.page.items);
cursor.unlock(() => {});
});
});
```

i get

```
[ { key: 'rdf/3/A', record: 'rdf/3/A', heft: 60 } ]
```

it seems like both the key and the record get set to the same thing and the data in the record is lost?

any idea whats going wrong there?

thanks!

Start by reproducing the shown Strata create, mutator, insert, open, and iterator sequence, then inspect the resulting cursor.page.items. Trace how the inserted key and record are stored and restored; the issue is done when reopening the tree preserves the record data instead of replacing it with the key.

Written by the indexing model from the issue text.