fix raise in exception with jump

add_ensure_iseq() adds ensure block to the end of
jump such as next/redo/return. However, if the rescue
cause are in the body, this rescue catches the exception
in ensure clause.

  iter do
    next
  rescue
    R
  ensure
    raise
  end

In this case, R should not be executed, but executed without this patch.

Fixes [Bug #13930]
Fixes [Bug #16618]

A part of tests are written by @jeremyevans https://github.com/ruby/ruby/pull/4291

test/ruby/test_exception.rb

@@ -78,6 +78,66 @@ class TestException < Test::Unit::TestCase
     assert(!bad)
   end
 
+  def test_exception_in_ensure_with_next
+    string = "[ruby-core:82936] [Bug #13930]"
+    assert_raise_with_message(RuntimeError, string) do
+      lambda do
+        next
+      rescue
+        assert(false)
+      ensure
+        raise string
+      end.call
+      assert(false)
+    end
+
+    assert_raise_with_message(RuntimeError, string) do
+      flag = true
+      while flag
+        flag = false
+        begin
+          next
+        rescue
+          assert(false)
+        ensure
+          raise string
+        end
+      end
+    end
+  end
+
+  def test_exception_in_ensure_with_redo
+    string = "[ruby-core:82936] [Bug #13930]"
+
+    assert_raise_with_message(RuntimeError, string) do
+      i = 0
+      lambda do
+        i += 1
+        redo if i < 2
+      rescue
+        assert(false)
+      ensure
+        raise string
+      end.call
+      assert(false)
+    end
+  end
+
+  def test_exception_in_ensure_with_return
+    @string = "[ruby-core:97104] [Bug #16618]"
+    def self.meow
+      return
+      assert(false)
+    rescue
+      assert(false)
+    ensure
+      raise @string
+    end
+    assert_raise_with_message(RuntimeError, @string) do
+      meow
+    end
+  end
+
   def test_errinfo_in_debug
     bug9568 = EnvUtil.labeled_class("[ruby-core:61091] [Bug #9568]", RuntimeError) do
       def to_s