Dan req1

Dan noticed some odd behavior with walker. See his note below. I was able to mitigate both bugs (or it appears so now) with this patch.

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Hey Pete, could you look at two more things real quick for me, things I found prepping for this walker presentation tomorrow.

1) Starting with an empty database, I did `walker seed -u http://turnitin.com` and then `walker dispatch`, and as expected it dispatched one link, which I see in the database. But, the console shows 0 links dispatched. I think it's because the dispatched link has no previous crawl time and is being counted in model.go as uncrawled, and we're leaving that number out.

2) Then I ran `walker fetch` to do a single fetch and got: "Failed storing fetch results: marshal bigint: value 14947298106726739655 out of range" You could probably reproduce it yourself; I'm not sure why it's an error because that number does seem to be within the range of a 64 bit integer.

Is fr.FnvFingerprint a uint64 type? If so could we move the conversion over to where we generate the has, and change the type of FnvFingerprint to int64? Seems like that'll make us less likely to have to cast/convert in other places. Unless there's a good reason not to that I'm missing.