Display URL as part of HTTP error messages

[msabramo]

It seems convenient to include the URL in the error message in case you get an unexpected error.

E.g.:

In [1]: import requests

In [2]: resp = requests.get('http://www.google.com/eofdfdfdfdfd')

In [3]: resp
Out[3]: <Response [404]>

In [4]: resp.raise_for_status()
---------------------------------------------------------------------------
HTTPError                                 Traceback (most recent call last)
<ipython-input-4-00e7077cfb5b> in <module>()
----> 1 resp.raise_for_status()

/Users/marca/dev/git-repos/requests/requests/models.py in raise_for_status(self)
    835
    836         if http_error_msg:
--> 837             raise HTTPError(http_error_msg, response=self)
    838
    839     def close(self):

HTTPError: 404 Client Error: Not Found for url: http://www.google.com/eofdfdfdfdfd

[Lukasa]

Seems reasonable enough to me. I'm happy to take this. @sigmavirus24?

[sigmavirus24]

Seems like a good UX improvement to me. 👍