Provide wxApp::StoreCurrentException() implementation for C++11.

When using C++11 we can provide implementations of wxApp::StoreCurrentException()
and RethrowStoredException() ourselves and thus make catching exceptions outside
of the event loop work by default.

Do this and update the documentation and the sample to reflect it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77470 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/except/except.cpp

@@ -94,6 +94,10 @@ public:
     // 2nd-level exception handling helpers: if we can't deal with the
     // exception immediately, we may also store it and rethrow it later, when
     // we're back from events processing loop.
+    //
+    // Notice that overriding these methods is not necessary when using C++11
+    // as they have a perfectly serviceable implementation inside the library
+    // itself in this case.
     virtual bool StoreCurrentException() wxOVERRIDE;
     virtual void RethrowStoredException() wxOVERRIDE;