Log Message:
Update chat/ejabberd to 15.09.

### Major changes
- Added OAuth delegation framework
- Preliminary OAuth and HTTP based ejabberd API
- X-AUTH2 authentication mechanism,
- MAM now can store MUC room
- MSSQL: improved schema, simplified config, and fixed support

*Note: ejabberd now requires erlang 17.1 or higher*

### Core improvements
- New `set_loglevel` admin command to ease changing loglevel.
- Configuration: allow to override main config file options with data
  from included files
- Improve S2S certificate checks
- Log TLS errors as debug messages only
- XEP-0198: new option "max_resume_timeout"
- XEP-0198: Improve handling of non-message stanzas
- ext_mod: Check external modules configuration on load
- ext_mod: Don't override custom configuration on module upgrade
- Several Elixir fixes
- Updated most translation languages

### Modules improvements
- Carbon Copy: Don't copy messages of type "normal" without body
- HTTP-Bind: More eye-candy mod_http_bind help page
- HTTP-Bind: Nameprep host name passed to http-bind before using in
- HTTP-Bind: Set disable caching headers in http-bind responses
- HTTP: pass stream management options defined in http listener to
  http-bind and websocket
- MAM: Add XEP-0359 to archived messages
- MAM: Add XEP-0313 v0.4 support
- MUC commands: Changed argument names in two commands
- MUC commands: Fix and document create_rooms_file and destroy_rooms_file
- MUC hooks: added muc_filter_presence
- MUC hooks: renamed muc_filter_packet to muc_filter_message
- MUC logging: check for hint
- Multicast: many improvements in the source code
- SIP: Do not crash SIP authentication on SCRAMed passwords

### Packaging
- Remove bashisms in join_cluster leave_cluster and postinstall scripts
- Allow root to run join_cluster and leave_cluster
- Allow building an ejabberd release with mix and elixir release manager
- Allow installing as root
- Fix Debian/Ubuntu package
- Rename idna to ejabberd_idna
- Improve 'make install' to remove useless failure cases