Reworked error handling in server, client and filer (again :( ). We definitely...

Reworked error handling in server, client and filer (again :( ). We definitely have to support multiple errors so let's do it right.  Error now contains list of errors.  Got rid of "detail" section everything now goes directly within particular error.  Error can bear "events" attribute for list of sent events concerned (or none if all sent events erred). Streamlined error logging.
Server now retries if MySQL went away.
Response result now gets properly encoded if Unicode appears somehow (however that's just fighting symptoms, should get more thorough fix).