xwin sets ROOTLESS_PROTECT_ALPHA to "NO": bug?

[Jamey Sharp]

The generic rootless layer can be built to preserve an alpha channel
for depth 24 images stored at 32 bits per pixel. It does this if
rootlessConfig.h defines ROOTLESS_PROTECT_ALPHA; it doesn't matter
what it's defined to.

When the server is built on Windows, ROOTLESS_PROTECT_ALPHA is defined
to NO, so rootless will protect the alpha channel. Counter-intuitive
to say the least.

Does Xwin need to preserve the alpha channel of its top-level windows,
or should the relevant line of rootlessConfig.h be changed to "#undef
ROOTLESS_PROTECT_ALPHA"?

I think rootless does more work than necessary if
ROOTLESS_PROTECT_ALPHA is turned off, presumably because that case
isn't actually being tested. It can probably be simplified if this
matters.

Jamey