attempting to get fdb-go working with go1.3

Don't merge without careful review, I just hacked around until I got the tests passing on my mac. 

The local channel variable (in `fdb_future_block_until_ready`) didn't seem to properly stick around after sending it to C--it probably has to do with "improvements" to the escape analysis, but I'm honestly not fully sure why it seems to work this way, so it's definitely not a thorough fix. 

I also cleaned up some warnings in `go vet` with regard to pointer conversions and uintptr.

Hope this helps...