Do not silence download errors when request errback raises an exception
Do not log IgnoreRequest exceptions as download failures
.remove_namespaces(): remove namespaces on elements' attributes
Merge pull request #423 from nramirezuy/defaultheaders-multispider

defaultheaders multi spider support removed
fix doc typo
Merge pull request #416 from redapple/attrnamespaces

.remove_namespaces(): remove namespaces on elements' attributes
Fix start_requests lazyness and early hangs

- Removes new public methods added by #330 to Crawler and CrawlerProcess
- Add test for start_requests lazy evaluation
- Fix and test hangs when start_requests erroed before returning the generator
- Add test when start_requests fails while generating requests
- Simplify Crawler and CrawlerProcess implementation taking in count
  that only one spider can be attached per Crawler. As required by SEP-019
- "scrapy settings" command do not require starting a Crawler anymore
Fix AlreadyCalledError replacing a request in shell command. closes #407
IPython refuses to update the namespace. fix #396

IPython embedding code borrowed from https://github.com/mitsuhiko/werkzeug/pull/85
Add 0.18.4 release notes

Conflicts:
	docs/news.rst
Merge pull request #418 from nramirezuy/engine-multispider

engine multispider support removed
Merge pull request #380 from dangra/dont-log-ignorerequest

Dont log IgnoreRequest exception as download failure
added required option to settings module