Make Timeout::Error#exception with multiple arguments not ignore arguments

lib/timeout.rb

@@ -32,6 +32,7 @@ class Error < RuntimeError
     def self.catch(*args)
       exc = new(*args)
       exc.instance_variable_set(:@thread, Thread.current)
+      exc.instance_variable_set(:@catch_value, exc)
       ::Kernel.catch(exc) {yield exc}
     end
 
@@ -40,11 +41,11 @@ def exception(*)
       if self.thread == Thread.current
         bt = caller
         begin
-          throw(self, bt)
+          throw(@catch_value, bt)
         rescue UncaughtThrowError
         end
       end
-      self
+      super
     end
   end
 
@@ -84,7 +85,7 @@ def timeout(sec, klass = nil, message = nil, &block)   #:yield: +sec+
 
     message ||= "execution expired".freeze
 
-    if (scheduler = Fiber.current_scheduler)&.respond_to?(:timeout_after)
+    if Fiber.respond_to?(:current_scheduler) && (scheduler = Fiber.current_scheduler)&.respond_to?(:timeout_after)
       return scheduler.timeout_after(sec, klass || Error, message, &block)
     end
 
@@ -115,6 +116,7 @@ def timeout(sec, klass = nil, message = nil, &block)   #:yield: +sec+
       begin
         bl.call(klass)
       rescue klass => e
+        message = e.message
         bt = e.backtrace
       end
     else

test/test_timeout.rb

@@ -80,6 +80,14 @@ def test_exit_exception
     end
   end
 
+  def test_raise_with_message
+    bug17812 = '[ruby-core:103502] [Bug #17812]: Timeout::Error doesn\'t let two-argument raise() set a new message'
+    exc = Timeout::Error.new('foo')
+    assert_raise_with_message(Timeout::Error, 'bar', bug17812) do
+      raise exc, 'bar'
+    end
+  end
+
   def test_enumerator_next
     bug9380 = '[ruby-dev:47872] [Bug #9380]: timeout in Enumerator#next'
     e = (o=Object.new).to_enum