Ported Brute's severed tail floats beside him #11

In game, the ported Brute's severed tail floats beside him, near the rest of his tail.

An MHP3rd rig authors the severed tail (the carvable piece dropped when the tail is cut) on its own root chain: the Brute's bones 43–45 and the Zinogre's 46–50. The native Tigrex carries one too (bones 45–47), and leaves it unparented. rig.from_donor adopts the donor's chain onto bone 1, so it moves with the body. But its offsets are relative to the donor rig's origin, which sits at the hip, not the ground, so it lands beside the tail rather than on it. Today's build did the same.

• Find how the native keeps its severed tail out of sight until the tail is cut (a draw flag, a group, or the chain's pose): it does not hide it. The piece is the tail's tip, mesh record 1, and em75's ATTACH poses its chain on the tail every frame; at the cut TAIL_DROP masks mesh 1 and TAIL_SPAWN drops a copy on the floor
• Ship the port's chain the same way: the chain stays an unparented root, the tip goes in mesh record 1, mhfu.em_tip copies its carriers, and verify fails a one-mesh port
• Check the Zinogre's chain in game as well: the tail is whole in idle, walk and attack, and the tip drops 0.2 s after the cut
• Check the Brute, rebuilt, in game

Done when neither port shows a loose tail piece before its tail is cut.

Landed in #63.