This makes it so we can encode errors in HTTP headers so long as the
encoder did not write anything.
This also changes the behavior to encode the stats trailer even in the
event of an error.
Introduces the Statisticser interface which ResultIterators may
implement.
The HTTP implementation uses HTTP trailers to preserve the statistics.
This way we do not need to have all encoders and decoders support
statistics.
This modifies the `MultiResultDecoder` interface to accept an
`io.ReadCloser` so the `ResultIterator` can close the `io.Reader`
instead of doing it through a defer call. It then makes it so the
`Cancel()` method will close the reader or the reader will be
automatically closed when `More()` returns false.
The query service now handles some errors (not all) from the ifqld
service. This way, the transpiler, which uses the query service, can
report when it encounters an error from ifqld.
The transpiler will now correctly return errors in the JSON response.
Nathaniel Cook
Jonathan A. Sternberg
Adam