This actually applies to YUV formats with 9-16 bit depths. This hack is
disabled by default, and the VO will use 16 bit textures normally.
It can be enabled by passing the no16bit-textures option is passed to
vo_direct3d. Then the VO will use D3DFMT_A8L8 as texture formats for the
YUV plane (instead of D3DFMT_L16), and compute the sampled two color
values back into one.
In some cases it might be undesireable to use 16 bit texture formats. At
least some OpenGL drivers on Linux (Mesa + Intel) round values sampled
from 16 bit textures back into 8 bit, which loses 8 from 10 bit color
information when playing 10 bit formats. It is unknown whether there are
D3D9 drivers which do this, so this commit might be removed later.
