Avoid dropping events in wxDocParentFrameAnyBase in some circumstances.

Avoid dropping events in wxDocParentFrameAnyBase in some circumstances.

The code trying to avoid forwarding duplicate events to wxDocManager was over
eager and in some situations filtered out the events which hadn't been sent to
it yet and were, in fact, not handled at all. This could be seen, for example,
by running the docview sample with "--sdi" command line option, creating one
child frame and then trying to create another one from the parent frame menu:
this failed because the existence of a valid child was considered to be enough
for the event to have been already processed in it which was false in this case.

Unfortunately there is no obvious fix to this problem, notably because of the
very roundabout way the toolbar events are processed in MDI windows: the
toolbar itself is a child of the parent frame but the events from it are still
sent to the currently active child frame by wxMDIParentFrameBase. So we can't
rely on any kind of parent-of-originating-window checks.

Instead, remember the last event handled in the child and avoid processing the
same event in wxDocManager again. This should at least avoid the false
positives (like the one fixed by this commit), although it could still result
in false negatives (i.e. some duplicated events) if an event handler generated
other events while skipping the original one. This is a lesser evil though and
should be relatively rare in practice, so live with this ugliness until
someone comes with another idea of fixing the bug described above.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74919 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775