Add --suppress-repeated-stacktrace option

Relatead to https://github.com/fluent/fluentd/issues/221 issue.

Remaining discussion is dump message.
Current logs:

```
2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:154:rescue in emit_stream: emit transaction failed  error_class=RuntimeError error=#<RuntimeError: syslog>
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/plugin/out_stdout.rb:43:in `emit'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/match.rb:36:in `emit'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/engine.rb:151:in `emit_stream'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/engine.rb:131:in `emit'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/plugin/in_object_space.rb:111:in `on_timer'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/plugin/in_object_space.rb:37:in `call'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/plugin/in_object_space.rb:37:in `on_timer'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/cool.io-1.1.1/lib/cool.io/loop.rb:96:in `run_once'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/.rbenv/versions/2.0.0-p247/lib/ruby/gems/2.0.0/gems/cool.io-1.1.1/lib/cool.io/loop.rb:96:in `run'
  2013-12-04 15:05:53 +0900 [warn]: fluent/engine.rb:140:emit_stream: /Users/repeatedly/devel/fluent/fluentd/lib/fluent/plugin/in_object_space.rb:63:in `run'
2013-12-04 15:05:53 +0900 [error]: plugin/in_object_space.rb:113:rescue in on_timer: object space failed to emit error="foo.bar" error_class="RuntimeError" tag="foo" record="{...}"
2013-12-04 15:05:55 +0900 [warn]: fluent/engine.rb:154:rescue in emit_stream: emit transaction failed  error_class=RuntimeError error=#<RuntimeError: syslog>
  2013-12-04 15:05:55 +0900 [warn]: plugin/in_object_space.rb:111:on_timer: suppressed same stacktrace
```