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
from_crawler added to spiders
added ftp handler
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
DownloaderMiddleware.process_response docs fix

"returns an exception" -> "raises an exception"
Merge pull request #338 from kmike/patch-3

DownloaderMiddleware docs fix
fix a possible error in contracts post hook
command with multiple crawlers, fix check command
disable logging for scrapy check
allow passing arguments to tox

e.g. "tox -- scrapy.tests.test_contrib_loader" runs test_contrib_loader for Python 2.6 and 2.7
use tox deps instead of "manual" pip install; add lucid and precise environments to tox.ini
add django to test requirements and fix test_djangoitem for modern django versions