Created xpp and upp aliases in mover_PC() as suggested by Alejandro Duran
eliminated use of ALLOC_SHIFT in Alloc.h
Revert "Created xpp and upp aliases in mover_PC() as suggested by Alejandro Duran"

This reverts commit 01716bef194d1dd8e1c02ee9df73a18b22ab10f5.
It appears that the aliases were increasing the time to advance
particles by roughly 60% rather than decreasing the time by 50%.
The reason is unclear.