Fix typo.
WIP: Wrap DB time values.

Time values are stored in the DB either as strings (if they came from Go
space) or Unix timestamps (if they were generated by the Cypher
`TIMESTAMP()` function).

The `WrappedTime` type provides a `Scan` method which can deal with both,
and a `Value` method which provides the string version for writing to the
DB. Supporting the `Scanner` and `Valuer` interfaces seems to be the key to
database happiness.

There's still some work to do:

1. Adding the same key twice still crashes. I *think* that's because of
   another query that's crashing, but it could be because this code is
   broken.
2. I've only applied this to the `PubKey` type. It needs applying elsewhere.
3. The type is probably defined in the wrong file.