INT-2982 Add Syslog Inbound Channel Adapter

* Supports UDP/TCP syslog messages.
* See docbook patch for more information.

For reference see: https://jira.springsource.org/browse/INT-2982
Merge pull request #780 from garyrussell/INT-2982

* garyrussell-INT-2982:
  INT-2982 Add Syslog Inbound Channel Adapter