Blender Git Loki

Fix for bug #3414 provided by Lewis Saunders.

It appears that removing the 'int level' field from the
MemHead struct caused alignment issues for gcc builds of blender
on Irix (zr, who removed this field, commented that this problem
might occur, and sure enough it did happen). I've renamed the
field from 'level' to 'pad' to reflect that it has no meaning
beyond addressing alignment issues.