Add missing wxABI_VERSION checks and version script entries.

Newly overridden virtual methods must be taken in wxABI_VERSION checks as
otherwise any program using the class deriving from the one containing this
method would reference the method in the vtbl of that class and so become
ABI-incompatible with the earlier shared library versions.

Also add wxABI_VERSION guard around the entire wxSimplebookXmlHandler class
added in 3.0.2.

version-script.in

@@ -21,6 +21,16 @@
 # and once released its version cannot be changed.
 
 
+# public symbols added in 3.0.3 (please keep in alphabetical order):
+@WX_VERSION_TAG@.3 {
+    *wxDataViewRenderer*FinishEditing*;
+    *wxFloatProperty*DoGetAttribute*;
+
+    # This class was actually added in 3.0.2 but not tagged correctly in it, so
+    # do it here following the better late than never principle.
+    *wxSimplebookXmlHandler*;
+};
+
 # public symbols added in 3.0.2 (please keep in alphabetical order):
 @WX_VERSION_TAG@.2 {
 	*wxGenericListCtrl*EndEditLabel*;