moving average block errors on NaN

[jacqui]

Apr 10 09:48:22 [ 4 ][ INFO ] map[Average:%!s(float64=NaN)]
2014/04/10 09:48:22 log.go:130: could not broadcast
2014/04/10 09:48:22 log.go:151: failed marshaling data into json

you can see this happen if you fire up the phone demo - the errors start immediately. they stop when the block starts receiving data from phones (e.g., valid numbers).

[jacqui]

I made some progress on this issue, but unfortunately rolling out the solution I came up with would require us to change all float64 types to a new type (jsonFloat) wherever we want to properly handle NaN's in json. I checked it into a branch on my fork instead. To be continued, later...