EXT-2974 Alpha mask textures not applied immediately

Eyelashes were causing the avatar's head to disappear on a non-cached
outfit if you created an alpha mask object through the appearance editor
even though you didn't select the head to be invisible. This would not
affect the baked texture, only the local composite.

No clue exactly why the symptom was what it was, but the way we were
using eyelashes was the source of the problem. Moving the special-case
eyelashes to an alpha mask layer fixes the issue.

 -Nyx