change throw calls to raise

@@ -16,7 +16,7 @@ module DsAdmin::Storage
   end
 
   def read
-    throw "#{self.class}: read not implemented"
+    raise "#{self.class}: read not implemented"
   end
 
   ##
@@ -24,7 +24,7 @@ module DsAdmin::Storage
   # entry.
   #
   def write(model)
-    throw "#{self.class}: write not implemented"
+    raise "#{self.class}: write not implemented"
   end
 
   def config_key