[decoder] graceful accept uint64 values if they're sent as int64 for ids

[palazzem]

What it does

In JRuby interpreter, unsigned int are sent as int type (Java related type system). This patch will handle IDs so that they're cast from int to uint.

[zaccari]

Thank you putting this together. I built the latest version of the trace agent with this code change to see if it resolved the issue for our JRuby 9.1.5.0 application. The error in the trace-agent.log was (pre merging this):

2017-02-22 12:56:45 ERROR (receiver_logger.go:21) - error when decoding msgpack traces

With this change I now see:

2017-02-22 12:45:00 ERROR (receiver_logger.go:23) - cannot decode v0.3 traces payload: msgp: attempted to decode type "int" with method for "uint"

I'm attempting to debug the issue locally, I'll let you know if I'm able to resolve it. In the mean time do you have any suggestions as to why the new error is being thrown?