I'm pretty sure it's still:
Code:
yourtexture:SetTexture("Interface/MainMenuBar/UI-MainMenuBar-EndCap-Dwarf")
There's also a lion motif:
Code:
yourtexture:SetTexture("Interface/MainMenuBar/UI-MainMenuBar-EndCap-Human")
There's only the one of each so you will to flip the texture with SetTexCoord() for the opposite end.