code: public String getMapProperty(String propertyName, String def) {
  		if (props == null)
  			return def;
  		return props.getProperty(propertyName, def);
  	}
docs: Get a property given to the map. Note that this method will not perform
  well and should not be used as part of the default code path in the game
  loop.
  
  @param propertyName
  The name of the property of the map to retrieve
  @param def
  The default value to return
  @return The value assigned to the property on the map (or the default
  value if none is supplied)