Merge another change from team/russell/events ...

DUNDi uses a concept called the Entity ID for unique server identifiers.  I have
pulled out the handling of EIDs and made it something available to all of Asterisk.
There is now a global Entity ID that can be used for other purposes as well, such
as code providing distributed device state, which is why I did this.  The global
Entity ID is set automatically, just like it was done in DUNDi, but it can also be
set in asterisk.conf.  DUNDi will now use this global EID unless one is specified
in dundi.conf.

The current EID for the system can be seen in the "core show settings" CLI command.
It is also available in the dialplan via the ENTITYID variable.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@121439 65c4cc65-6c06-0410-ace0-fbb531ad65f3