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
doc: Response.replace() cannot take meta argument

>>> response.replace(meta={'foo':1})
Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/srv/scrapy/scrapy-fork/scrapy/scrapy/http/response/text.py", line 45, in replace
    return Response.replace(self, *args, **kwargs)
  File "/srv/scrapy/scrapy-fork/scrapy/scrapy/http/response/__init__.py", line 77, in replace
    return cls(*args, **kwargs)
  File "/srv/scrapy/scrapy-fork/scrapy/scrapy/http/response/text.py", line 22, in __init__
    super(TextResponse, self).__init__(*args, **kwargs)
TypeError: __init__() got an unexpected keyword argument 'meta'
doc: remove trailing spaces
Document CrawlSpider.parse_start_urls method
Merge pull request #321 from barraponto/document_crawlspider_parse_start_urls

Document CrawlSpider.parse_start_urls method
rename http11 handler methods and split latency and timeout check
fix download_timeout for servers that returns response headers but hangs sending its body
do not skip image tests and set a fixed pyOpenSSL version
show a meaningful skip message for image tests
fix helpers used to sign S3 requests with boto connections
Merge pull request #275 from stav/doc

doc: Response.replace() cannot take meta argument
added a bit more documentation on how to close the reactor when running scrapy from a script
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)