Matching on bodies uses urllib.parse.parse_qs(), which fails to handle
UTF-8+URLEncoded POST bodies when the input is `bytes` rather than `str`,
causing matching to fail..
Fixed this by always doing decode('ascii') on URLEncoded POST bodies first.
Previously request.headers was a normal dict (albeit with the
request.add_header interface) which meant that some code paths would do
case-sensitive matching, for example remove_post_data_parameters which
tests for 'Content-Type'. This change allows all code paths to get the same
case-insensitive treatment.
Additionally request.headers becomes a property to enforce upgrading it to
a CaseInsensitiveDict even if assigned.
It shouldn't matter whether the request body comes from a file or a
string, or whether it is passed to the Request constructor or assigned
later. It should always be stored internally as bytes.
When converting objects to body, dicts and sets order can change
resulting in a different but same body. This fixes the issue by
comparing the enclosed data in the body rather than the body itself
while still allowing raw body matching with the raw_body matcher.
This commit not only changes the default method of matching requests
(just match on method and URI instead of the entire request + headers)
but also allows the user to add custom matchers.
