Map:
D3DFMT_L16 -> GL_LUMINANCE16_EXT
D3DFMT_A16B16G16R16 -> GL_RGBA16_EXT
as Raphael suggested.

Also increase the returned Bpp for unknown and unhandled formats from
4 to 8 bytes - this part fixes segfault in the F.E.A.R demo. It now
shows some flashy graphics before it dies again :)