Three more attempts to get metal look.

  Three more attempts to get metal look.
     - Added a few flags for inheriting background.
     - Added wxWindow param to wxR::DrawBackground()
     - Added wxR::DrawButtonSurface()
     - Removed wxR::DrawBackground() from wxR::DrawButtonBorder()
     - Adde DrawMetal to Metal theme
  Fixed minor bug in wxGTK scrollbar.
  Changed code in wxX11 wxTLW so that startup flicker no
    longer occurs in wxFrame.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@15136 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775