key bugs resolved:

- make sure that we only push things into _writtenAwaitingResponse until we have actually written them; they are allowed to throw certain errors *before* write, which breaks the queue completely
- ensire that MOVED redirects are sents as "internal call"; this means that if this is a new server, it can be queued rather than dropped
- allow MOVED code to select a server that isn't "up" yet

additional tweaks:

- change accessibility on WriteImpl to ensure everything goes via WriteTo
- renamed some methods to clarify what the lock status is: ...InsideWriteLock, ...TakingWriteLock, etc
- fix bug where ExportConfiguration can fail if a result is nil (although this might be a false outcome)
- why did StringGetWithExpiryMessage specify NoRedirect?
- clarify messages for ProtocolFailure and MOVED