Make wxBU_EXACTFIT fir the button text more exactly.

Too big margins were added for the buttons with wxBU_EXACTFIT style making
them larger than strictly necessary. Reduce the margins to make them really
as small as possible.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68922 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/private/button.h

@@ -44,7 +44,8 @@ void UpdateMultilineStyle(HWND hwnd, const wxString& label);
 // flags for ComputeBestSize() and GetFittingSize()
 enum
 {
-    Size_AuthNeeded = 1
+    Size_AuthNeeded = 1,
+    Size_ExactFit   = 2
 };
 
 // NB: All the functions below are implemented in src/msw/button.cpp