Fixed linear regalloc bug, dropped some tracing code

Fixed linear regalloc bug, dropped some tracing code
o The linear-scan register allocator sometimes allocated a block
  before allocating one of its predecessors, which could lead
  to inconsistent allocations. Now, we allocate a block only
  if a predecessor has set the "incoming" assignments for the block
  (or if it's the procedure's entry block).
o Also commented out some tracing code on the new codegen path.