# Get layer class from TileCache::Layers for the specified type,
# raises TileCache::InvalidConfiguration if no class has been found
def layer_class_for(type)
	class_name = type.sub(/\ALayer/, "") # once and only in the beginning
	raise NoSuchLayer, "Invalid layer type attribute: #{type}" unless Layers.const_defined?(class_name) # I assume we are within TileCache
	TileCache::Layers.const_get(class_name)
end