Always use 32bpp image lists.

Always use 32bpp image lists.

Using 32bpp image lists (ILC_COLOR32) is required as we need to be able to put
32bpp bitmaps in them and results in better (albeit still broken, see #9050)
display when the display depth is < 32.

This change was tested under Windows 2000, 2003 and Vista in 8 (Win2k-only),
16 and 32bpp display depth modes.

Closes #11031.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61853 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775