Fix a memory leak in the breakpoint window.

Parent message alerts by the active window.  This way if another window is open it isn't pushed behind the main window.  We probably should parent the message alerts by the calling window instead, but this may be good enough.
Make sure there is only one instance of some modeless windows (Cheats Manager and Net Play).


git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@7257 8ced0084-cf51-0410-be5f-012b33b47a6e

Source/Core/DolphinWX/Src/NetWindow.h

@@ -87,6 +87,8 @@ public:
 	void OnMsgStartGame();
 	void OnMsgStopGame();
 
+	static NetPlayDiag *&GetInstance() { return npd; };
+
 private:
     DECLARE_EVENT_TABLE()
 
@@ -108,6 +110,8 @@ private:
 	std::vector<int>	m_playerids;
 
 	const CGameListCtrl* const m_game_list;
+
+	static NetPlayDiag* npd;
 };
 
 DECLARE_EVENT_TYPE(wxEVT_THREAD, -1)