Add wxApp::StoreCurrentException() and RethrowStoredException().

These methods can be used to ensure that the exceptions thrown from event
handlers are safely rethrown from the code dispatching the events once the
control flow gets back there.

This allows to work around the problem with not being able to propagate
exceptions through non-C++ code and can be used, for example, to catch
exceptions thrown by the handlers invoked from inside wxYield() by a try/catch
block around wxYield() -- something that didn't work before, update the except
sample to show that it does work now.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77468 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -32,6 +32,7 @@ Changes in behaviour which may result in build errors
 
 All:
 
+- Add wxApp::StoreCurrentException() and RethrowStoredException().
 - Allow iterating over wxCmdLineParser arguments in order (Armel Asselin).
 - Add wxScopedArray ctor taking the number of elements to allocate.
 - Add wxDynamicLibrary::GetModuleFromAddress() (Luca Bacci).