Reimplement db created events
Notify the ddoc cache when design docs change
Throw unknown_error for non standard errors

Right now unless you throw an error with the key forbidden or
unauthorized, we throw a stack trace back at you. This will at least let
you throw a string as an error message.

Whether or not we should return unknown_error: Message or throw an error
saying invalid error format in the validate_doc_update function is
debateable.
Switch to using is_binary guard
Fix views for node-local databases

Simple fix matches on `<<"shards/", _/binary>>` to detect if it should
use a Fabric call or open a local database.

BugzId: 14565
_key is confusing
Only use the ddoc cache for sharded dbs
Fix new _stats with added 'working properly' feature
Remove message when adding async open listeners

This log message isn't particularly useful.
Depend on new config app
Fix _sum reducer for objects with missing keys

BugzId: 17391
Update and refine comment regarding spawn

BugzID: 13179
Middle ground on logging db openers

Rather than get too complicated with timers for each db open we'll just
silence if there's less than some smallish number of clients. And if
that threshold is exceeded we'll also log the total number of clients.
Use the new config app instead of couch_config