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

This makes:

  raise(Timeout::Error.new("hello"), "world")

raise a TimeoutError instance with "world" as the message instead
of "hello", for consistency with other Ruby exception classes.

This required some internal changes to keep the tests passing.

Fixes [Bug #17812]

Author: jeremyevans

lib/timeout.rb

@@ -32,19 +32,21 @@ class Error < RuntimeError
     def self.catch(*args)
       exc = new(*args)
       exc.instance_variable_set(:@thread, Thread.current)
-      ::Kernel.catch(exc) {yield exc}
+      catch_value = Object.new
+      exc.instance_variable_set(:@catch_value, catch_value)
+      ::Kernel.catch(catch_value) {yield exc}
     end
 
     def exception(*)
       # TODO: use Fiber.current to see if self can be thrown
       if self.thread == Thread.current
         bt = caller
         begin
-          throw(self, bt)
+          throw(@catch_value, bt)
         rescue UncaughtThrowError
         end
       end
-      self
+      super
     end
   end
 
@@ -115,6 +117,7 @@ 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