version: update version to mpich-4.3.0a1

Mark the mversion as 4.3.0a1.

Add changelog entry for ucx dynamic process and MPI_MAX_PORT_NAME.

CHANGES

@@ -1,3 +1,11 @@
+===============================================================================
+                               Changes in 4.3
+===============================================================================
+# ch4:ucx now supports dynamic processes. MPI_Comm_spawn{_multiple} will work.
+  MPI_Open_port will fail due to ucx port name exceeds current MPI_MAX_PORT_NAME
+  of 256. One can work around by use an info hint "port_name_size" and use a
+  larger port name buffer.
+
 ===============================================================================
                                Changes in 4.2
 ===============================================================================

maint/version.m4

@@ -14,7 +14,7 @@
 # changing this by playing with diversions, but then we would probably be
 # playing with autotools-fire.
 
-m4_define([MPICH_VERSION_m4],[4.2.0b1])dnl
+m4_define([MPICH_VERSION_m4],[4.3.0a1])dnl
 m4_define([MPICH_RELEASE_DATE_m4],[unreleased development copy])dnl
 
 # For libtool ABI versioning rules see: