Should be able to set negative times for dates before 1/1/1970

From the mailing list:

```
I've tried to create records before epoch (1/1/1970) by posting data like

[ { "name": "test", "columns": ["time", "value"],
 "points": [  [-1, 1], [-2, 2] ] } ]

This doesn't result in an error but queries for the data return nothing. I suspect InfluxDB doesn't support dates prior to 1/1/1970. Is this right?
```

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