Use equally-sized buttons in wxMSW horizontal toolbars

Only use TBSTYLE_AUTOSIZE, adjusting each button to the size it really needs,
for the toolbars with wxTB_HORZ_LAYOUT style as they don't have any uniform
button size anyhow.

src/msw/toolbar.cpp

@@ -1095,7 +1095,7 @@ bool wxToolBar::Realize()
                 // automatically according to the size of their bitmap and text
                 // label, if present. They look hideously ugly without autosizing
                 // when the labels have even slightly different lengths.
-                if ( !IsVertical() )
+                if ( HasFlag(wxTB_HORZ_LAYOUT) )
                 {
                     button.fsStyle |= TBSTYLE_AUTOSIZE;
                 }