urllib2.py version 1.72 uses capitalize() on HTTP
header names. This results in headers like "User-agent"
instead of "User-Agent". The former form is used
throughout the module as well. This is incorrect.

In this patch I've removed the capitalize() calls and
used the correct form throughout both the module.and
the tests.

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The form "User-agent" is not incorrect, merely unconventional 
(see RFC 2616, section 4.2).

The .capitalize() calls were introduced to make headers 
properly case-insensitive while keeping old code working -- 
see patch 649742.

The problem has arisen because urllib2 recently switched to 
using httplib.HTTPConnection (and the .request() method in 
particular, which sends Content-Length automatically) where 
previously it used httplib.HTTP (which did not send Content-
Length automatically).

The real problem is that httplib.HTTPConnection.request() 
sends some headers without checking that they aren't 
already in the explicitly requested headers.  I have submitted 
patch 997626 to fix this.

Thanks for reporting this, Johannes!

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Thanks for the explanation, self-rejecting this one.