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

doc/tex/asterisk-conf.tex

@@ -124,6 +124,11 @@ languageprefix = yes | no
 ;           eh. on SMB/CIFS mounts
 lockmode = lockfile | flock
   
+; Entity ID.  This is in the form of a MAC address.  It should be universally
+; unique.  It must be unique between servers communicating with a protocol
+; that uses this value.  The only thing that uses this currently is DUNDi,
+; but other things will use it in the future.
+; entityid=00:11:22:33:44:55
 
 [files]
 ; Changing the following lines may compromise your security

doc/tex/channelvariables.tex

@@ -795,6 +795,7 @@ ${TRANSFER_CONTEXT}      Context for transferred calls
 ${FORWARD_CONTEXT}       Context for forwarded calls
 ${UNIQUEID}            * Current call unique identifier
 ${SYSTEMNAME}          * value of the systemname option of asterisk.conf
+${ENTITYID}            * Global Entity ID set automatically, or from asterisk.conf
 \end{verbatim}
 
 \subsection{Application return values}