Fix back in time bug.

Fixes a bug where the points occasionaly go backwards in time, rather than
forwards. The timestamp of the first and last point in a stream are sent,
rather than just the first, in order to more correctly calculate timeing
data. This should no longer be an issue.

Another small bug was also fixed regarding checksums. Occasionally,
packets would have incorrect calculated checksums if they contained an ESC
or End Of Packet character within their data stream, and were not
correctly byte aligned. (two values overlap in a single byte, resulting in
ESC or EOP) There may be other cases as well that were fixed.
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