Changes

I am committing code that effectively ignores the values of certain
zt stats at the ghost level by setting them to 0. This is done to
allow for bit-for-bitness comparisons between the master branch
and the clubb_ghost_exorcism branch.

Technically, since zt stat file output at the irrelevant ghost
level is changed for some variables, this commit is BIT_CHANGING.

Effectively, this commit doesn't change squat in terms of model results.

I am moving the advance_xm_wpxp setting of xm(1) = xm(2) from the
end of xm_clipping_and_stats to the very end of advance_xm_wpxp, right
before the return to advance_clubb_core. The reason I am doing this
is the nudging was done after setting xm(1) = xm(2) and would alter
the results. This is no longer the case, as setting xm(1) = xm(2)
is now being done after nudging.

This is being done in advance of removal of the ghost point from CLUBB.
This helps ensure a bit-for-bit match between the ghost exorcism branch and the
master branch.

This commit technically alter fields such as um, vm, um_bt, vm_bt,
wpup2, wpvp2, and shear at level 1 only. Thus, this commit is
technically BIT_CHANGING.

Effectively, once again, this commit doesn't change squat.