added wxDIB::Save() and wxDIB to/from wxBitmap) conversions, use them instead of the old C functions (the latter were removed, there is no old code left any more)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@19744 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/bitmap.cpp

@@ -487,7 +487,6 @@ bool wxBitmap::DoCreate(int w, int h, int d, WXHDC hdc)
         hbmp = dib.Detach();
 
         GetBitmapData()->m_depth = d;
-        GetBitmapData()->m_hasAlpha = d == 32; // 32bpp DIBs have alpha channel
     }
     else // create a DDB
     {