Removed the SaveBG hack. The real incompatibility is that the MemoryDC

Removed the SaveBG hack.  The real incompatibility is that the MemoryDC
is not automatically cleared to the BG colour of the window when a
temporary bitmap is used.

Inlined the rest of the methods, there really is no reason for them not
to be.  (will remove dcbuffer.cpp as soon as I figure out the bakefiles)

Do device to logical transforms in UnMask.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@25859 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775