Feature request: Error handling in void *produce()

[65278]

On Bagger, tables were not created (create_partition.pl stalling forever on some broken instance). Since the result of PQputCopyData is not checked, this condition wasn't noticed until half a day later.

It'd be nice if the condition was communicated and schaufel shut down, so silent message combustion doesn't happen anymore. Here's what that looks like:

2018-07-17 08:56:06 UTC STATEMENT:  COPY bagger_32_5436_10.data FROM STDIN
2018-07-17 08:56:06 UTC ERROR:  relation "bagger_32_5436_10.data_callback_worker_event_2018_07_17_08" does not exist at character 13

And here's main.c on the issue:

157             //TODO: check success
158             producer_produce(p, msg);