Better error response when bucket size limit is reached.

[andrewxhill]

Currently getting a confusing error when you pass the 4GiB limit on buckets.

Error on buck push: Stream terminated by RST_STREAM with error code: INTERNAL_ERROR

[andrewxhill]

i verified that locally i'm getting the right error

Push 67 changes: y█
+ dbny3.png:  0 B / 8.04 kB [                                                        ]   0%
> Error! Max bucket size exceeded

[andrewxhill]

damn. tricked me again