Log Message:
Update chat/ejabberd to 17.04.
Make the Redis support unconditional (no extra dependencies).

Changes in 17.04:

Admin
- Add more examples on config template
- Generate ejabberd lib dir when not available in code server
- Set default prefix to /usr/local
- Start supervisors after ext_mod
- Don't log warning on successful ping reply
- New muc_register_nick command

Core
- Deprecate jlib.erl in favor of misc.erl
- Add support for file-based queues
- ejabberd_sm: Fix routing of headline and groupchat messages
- Fix c2s connection close on demand
- Improve overloaded S2S queue processing

Databases
- Improve Redis related code
- Add Redis pool support
- Improve logging of Redis errors
- Add Redis and SQL as mod_proxy65 RAM backends
- Add Redis and SQL as mod_carboncopy RAM backends
- Add Redis and SQL as mod_bosh RAM backends
- Add Redis and SQL as router RAM backends
- Add SQL as mod_muc RAM backend
- Remove obsolete Pubsub mnesia migration calls

Miscellany
- ejabberd_http: Expand @VERSION@ in custom headers
- ejabberd_http: Add "custom_headers" option
- mod_client_state: Queue stanzas of each full JID
- mod_http_upload: Don't add "Server" header line
- Pubsub: Refactor pubsub's get_last_items
- Pubsub: Fix PEP issues