Synced some code with TileZed.
Better memory management when running BMPToTMX.

MapManager frees 300x300 maps sooner.
Maps are purged before running BMPToTMX.
BMP images are freed as soon as possible (and before reloading changed maps).
Added Blend.exclude2 attribute to Blends.txt.

The exclude2 attribute is a list of tile/layer pairs.  If an existing map
tile matches one in exclude2, the blend tile is not applied.
Added "Show adjacent maps" option.
Q_UNUSED ftw.