Give an error if MapBaseXML.txt seems empty of layers.
LotsDock displays the filename suffix.
CellScene lot item tooltip displays the complete file path.
Fixed off-by-1 error with the size of .tbx maps in MapInfo.
Fixed MapManager not emitting mapFileChanged signal unless a map was loaded.

When a MapInfo points to a real file, the file's path is added to FileSystemWatch
even if the map wasn't loaded.  Since MapImageManager uses MapInfo to track
changes to map files, it is important to emit the mapFileChanged signal even
when a map isn't loaded.
The 'assign maps to world' step of BMPToTMX is now undoable.
Optimized BMPToTMX a bit by mapping layers to Blends.
Added "Compress tile layer data" option to BMPToTMX.

When checked, generated .tmx files use Base64Zlib compression.  Otherwise,
they use CSV format.
Use QDir::toNativeSeparators in several places.
Allow the preferences dialog to be used when there is no open world.

PreferencesDialog doesn't actually use the current document.
Fixed "tmxexportdir" set to the .pzw file's directory not being saved/restored properly.

If the TMX export directory was the same as the .pzw file's directory, then
the relative path was "".  Now I save an empty relative path as ".".
Fixed warnUnknownColors setting being assigned to assignMapsToWorld.
The default Tiles Directory is ../Tiles or ../../Tiles.

Instead of looking only for ../Tiles we also look for ../../Tiles.
Also, the path is cleaned of "..".
Added MapImage::isLoaded(), don't display unloaded map thumbnail in the Maps Dock.

If an map image hasn't been loaded by a worker thread yet, don't display the
image in the Maps Dock.  It will be displayed when the mapImageChanged signal
is emitted.
Delete all the image-reader threads when deleting MapImageManager.
MapManager reads only the first 1024 bytes of a map file when getting info.

I *think* the QXmlStreamReader reads the whole file in.
Use QDir::toNativeSeparators when displaying the Maps Dock's current directory.