add response arg to item_dropped signal handlers
#710
Merge remote-tracking branch 'upstream/master'
better call to parent class
update a link reference
set the exit code to non-zero when contracts fails
Merge pull request #727 from tpeng/fix-scrapy-check-exitcode

set the exit code to non-zero when contracts fails
DOWNLOADER setting
DOWNLOADER setting
limit Twisted support to pre-14.0.0 while #718 is fixed
fix tests after changes introduced by scrapy/w3lib#21
force installation of w3lib and queuelib for trunk env
Merge pull request #738 from chekunkov/downloader_setting

Downloader setting
Merge pull request #726 from nyov/fix

some cosmetics
Merge pull request #724 from rafallo/master

item_dropped signal should pass response arg as item_scraped does
improvements to scrapy check/contracts

* report number of contracts run and time spent (similar to unittest)
* exit with code 1 if there are failures (similar to unittest)
* capture and report errback errors (twisted or mw errors)
* capture and report callback errors (exceptions raised by spider)