Explicitly check if an object is a class is pydispatch.

* This is to fix a disagreement in between CPython and PyPy.
* https://gist.github.com/4220533
PEP8 on pydispatch/robustapply.py
callLater must happens before timeout callback is added to avoid AttributeError
fix import of deprecated http handler for S3 handler
remove wrong default httpcache
Merge pull request #326 from berendiwema/master

Include example of how to stop the reactor from script
removed request_received and added request_scheduled
Merge pull request #328 from nramirezuy/signals-request_scheduled

removed request_received and added request_scheduled
remove no deprecated request_scheduled signal

It will be replaced by more accurate scheduler signals (proposal will
come soon)
from_crawler added to spiders
added ftp handler
increase delay in test to avoid small time differences
offsite multispider support removed
pipeline media removed multispider support
Merge pull request #332 from nramirezuy/offsite-remove_multispider

offsite multispider support removed
Merge pull request #333 from nramirezuy/mediapipe-remove_multispider

pipeline media removed multispider support
feedexport removed multispider support
Merge pull request #334 from nramirezuy/feedexport-remove_multispider

feedexport removed multispider support
improve docs for DownloaderMiddleware.process_response
Merge pull request #337 from kmike/patch-2

improve docs for DownloaderMiddleware.process_response