Two fixes to referencing processing.

Two fixes to referencing processing.

First, ensure the transporter allocates from blocks on the scavenger
work queue.  Previously, the transporter could have objects allocated
in the free space of dequeued to-space blocks.  When this condition
occurs we unconditionally enqueue the block for re-scavenging.

Second, finish the implementation of large heap table scavenging and
add a verification routine for this root.

Change-Id: I5a9caf4b2824673a1f532c4e215c53f64a6a4627