doc: update CHANGES for new process addressing design

Add entry to note that we redesigned how process addressing (lpid) work
especially in Ch4. Ch3 merely made compatible and won't support true MPI
session nor improved efficiency in managing comm tables.

Author: hzhou

CHANGES

@@ -15,12 +15,19 @@
 # Yaksa is now maintained inside MPICH rather than as an external submodule.  
 
 # Added internal builtin datatypes and external builtin datatypes are mapped to
-internal types. For example, both MPI_INT and MPI_INT32_T are mapped to internal
-type MPIR_INT32. NOTE: direct usage of external MPI types are disallowed
-in MPICH internally. For example, use MPIR_INT_INTERNAL to replace direct usage
-of MPI_INT. Commonly used types include MPI_BYTE, MPI_CHAR, MPI_AINT, use
-MPIR_BYTE_INTERNAL, MPIR_CHAR_INTERNAL, MPIR_AINT_INTERNAL instead. There is no
-impact to users.
+  internal types. For example, both MPI_INT and MPI_INT32_T are mapped to internal
+  type MPIR_INT32. NOTE: direct usage of external MPI types are disallowed
+  in MPICH internally. For example, use MPIR_INT_INTERNAL to replace direct usage
+  of MPI_INT. Commonly used types include MPI_BYTE, MPI_CHAR, MPI_AINT, use
+  MPIR_BYTE_INTERNAL, MPIR_CHAR_INTERNAL, MPIR_AINT_INTERNAL instead. There is no
+  impact to users.
+
+# ADI: MPID_Comm_get_lpid removed. Lpids are looked up from the local_group and
+  remote_group in the MPIR_Comm struct.
+
+# ADI: MPID_Intercomm_exchange_map renamed to MPID_Intercomm_exchange and
+  parameters now include tag, context_id, and will perform context_id exchange
+  and lpid exchange.
 
 # Added MPI_LOGICAL1, MPI_LOGICAL2, MPI_LOGICAL4, MPI_LOGICAL8, and MPI_LOGICAL16.