Add drawBBox() method, and fix a number of BBox problems.

[dpvc]

Add drawBBox() method (for debugging), and fix a number of bounding box problems that it was able to demonstrate.

It turns out we don't want to replace the original bbox created for a wrapper (as it can cause loss of other data, like the L property), so we don't use BBOX.empty() in computeBBox() but instead add an empty() method to the bbox to set the w, h, and d values appropriately in the already existing BBoxes.

We use a new getSpace() method to compute bbox.L (the left spacing) when the object is created (since some bbox computations need it).

Since the bbox.L value is already computed, we use that to set the space attribute rather than the old SPACE array (which is no longer needed).

The rest of the changes are tweaks to get the bounding boxes or placement of things correct.

[zorkow]

lgtm.