Added BMPToTMX option to copy pixels to generated TMXs instead of placing tiles.
PNGBuildingDialog now correctly checks every tile for trees.

It used to only check 0_Vegetation, and wasn't even running BmpBlender.
MSVC 2012 fixes.
Switch to a cell's WorldDocument when closing the cell.

When multiple worlds are open, it is annoying when closing a cell to have a
unrelated world/cell become current.
Experiment with QThreadStorage in ZLevelRenderer::drawLayerGroup().
SpawnToolDialog sets the enabled state of the "remove" button appropriately.
LotFilesManager won't write "missing" tiles to .lot files.
Misc unimportant changes.
Updated dist.tcl for 32-/64-bit builds.