prepare 2.3.1 release

ChangeLog

@@ -57,3 +57,7 @@
  * improve what objects may participate in an address
  * clean up handled class/type combinations to current OSM usage
  * lots of bug fixes
+
+2.3.1
+
+ * fix parse error in replication state directories (fatal during setup)

configure.ac

@@ -1,4 +1,4 @@
-AC_INIT(Nominatim,2.2)
+AC_INIT(Nominatim,2.3.1)
 if git rev-parse HEAD 2>/dev/null >/dev/null; then
     AC_SUBST([PACKAGE_VERSION], [$PACKAGE_VERSION-git-`git rev-parse --short HEAD`])
 fi