Cleaned up the gui_core code. Also made it so that the gui event handler thread

isn't created at all unless some part of an application calls some of the
gui_core code.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402563

dlib/gui_core/gui_core_kernel_1.h

@@ -39,6 +39,7 @@
 #include "../queue.h"
 #include "../pixel.h"
 #include "../unicode.h"
+#include "../smart_pointers_thread_safe.h"
 
 
 namespace dlib
@@ -51,6 +52,7 @@ namespace dlib
     {
 
         LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM);
+        class event_handler_thread;
 
     }
 
@@ -164,6 +166,7 @@ namespace dlib
     class base_window
     {
         friend LRESULT CALLBACK gui_core_kernel_1_globals::WndProc (HWND, UINT, WPARAM, LPARAM);
+        shared_ptr_thread_safe<event_handler_thread> globals;
 
         HWND hwnd;
         DWORD style;