add an assert indicating that old code overriding OnExecute() must be updated with 2.9

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@53431 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -37,6 +37,8 @@ changes:
   to work with "wxChar *" before use "void *" now (some int parameters were
   also changed to size_t). While wxIPC_TEXT can still be used to transfer 7
   bit text, the new wxIPC_UTF8TEXT format is used for transferring wxStrings.
+  Also notice that connection classes should change the parameter types of
+  their overridden OnExecute() or override a more convenient OnExec() instead.
 
 
 wxODBC and contrib libraries removal