add a test.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15694 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bootstraptest/test_knownbug.rb

@@ -60,3 +60,7 @@ assert_equal 'ok', %q{
     :ok
   end
 }, '[ruby-core:15551]'
+
+assert_normal_exit %q{
+  sprintf("% 0e", 1.0/0.0)
+}