BuildingEd: Wall objects split rooms when creating RoomDefs.

A number of Mash's maps use Wall objects to split up a single room into
separate ones.  For example, a single bathroom is split into 2 by placing
a Wall object down the middle.  Previously, such rooms were viewed as a
single room when creating RoomDef objects.  Now Wall objects with non-none
interior wall tiles will split rooms.

Note: furniture objects in the "Walls" layer are ignored.
Fixed LotPackLayerGroup::orderedCellsAt() adding null entries to mTileByName.

Did this cause a crash? Can't remember!
Fixed LotPackWindow::tilePositionChanged() incorrect bounds check.
LotPackViewer: set initial world coordinates correctly.
Many changes to support compilation under Qt 5.1.1.
Remove "#include simplefile.h" from road.h, use reference to type instead.
Fixed crash with MapComposite's handling of mKeepFloorLayerCount.
Removed trailing separator from the main toolbar.
Call CompositeLayerGroup::synch() in CompositeLayerGroupItem::paint().

When a map changed on disk, MapComposite would call CompositeLayerGroup::setNeedsSynch(true)
as way of preventing CompositeLayerGroupItem() from painting the layer group
while the map was being reloaded.  This was fragile, and had recently been
changed so that affected layergroups cleared the list of map layers to prevent
accessing deleted map layers.

CompositeLayerGroupItem::paint() now calls synch() when needed, which fixes
flashing (such as when undoing adding a lot).
Fixed z-order of SubMapItems.
Re-enable CellScene::doLater() working at idle time.

doLater() was always supposed to delay expensive work until idle time, but
due to event processing during loadMap() causing crashes was changed to do
its work immediately.  Recent changes to handle delayed map loading seem to
have fixed this issue, so doLater() once again does its work at idle time.
Updated dist.tcl to remove EnableDeveloperFeatures.txt.
Don't show heightmap tool/command unless EnableDeveloperFeatures.txt is present.
Fixed repaint issue when adding/removing/moving Lots.

First, undid recent change where CompositeLayerGroupItem::paint() would call
synch(), that isn't ok because the bounds of the item might be out-of-date.

The real fix is to call doLater() before adding/moving QGraphicsItems so that
synch() gets called *before* the QGraphicsItems schedule their own redraw.
Closing LotPackWindow deletes the world etc to free up resources.
BMPToTMX sets error message when converting an image to 32bpp fails.