Add xpath suppot for FormRequest.from_response.
add error details when image pipeline fails
Merge pull request #202 from saxicek/master

Image pipeline error improvement
QPS bench server and a useful spider spider to generate requests
Remove concurrency limitation when using download delays and still ensure inter-request delays are enforced
Support sending requests trough multiples slots in QPS exmaple spider
Add 0.16.3 release notes
Update docs/topics/commands.rst

A short change.
Merge pull request #204 from LuanP/patch-1

Update docs/topics/commands.rst
fix pylint and pep8 warnings
Altering delay is enough to auto throttle downloads
core: move download slot assignment post middleware evaluation
core: drop download inactive slots and get slot key from meta
Merge pull request #206 from dangra/downloader-enhancements

AutoThrottle and Downloader enhancements
fix bug in scrapy parse command when spider is not specified explicitly. closes #209
Removing plural from httpcache stats' value names.
Add middleware support for real HTTP caching. Add httpcache setting to allow either real or dummy HTTP caching (for backwards compatibility it's set to use dummy cache by default).
Add middleware support for the 'no-store' Cache-Control directive.
Add cache storage support for real HTTP caching. Add real HTTP caching unit tests for both middleware and cache storage.
Updated the downloader middleware documentation to reflect changes introduced by the support for real HTTP caching.