Fix paste.exceptions.serial_number_generator.hash_identifier()

Use Message.items() method instead of HTTPMessage.headers attribute.

Fix bad reference to iterator variable

* Remove unused variables
* Remove unused imports
* Remove dead code

Rename duplicated uninstall() function to uninstall_stdin() and fix typo in
variable name (_oldstin => _oldstdin).

Use self.pos instead of an unknown pos variable.

instead of using wsgilib.parse_querystring() alias.

Remove a duplicated method, keep the implementation using ignore_wildcards.

* wsgi.input must be a binary file, not a text file
* Fix fixture.TestApp.__str__() on Python 3: decode body from UTF-8
  (with xmlcharrefreplace).
* Fix fixture.TestResponse.goto() on Python 3: regex must use bytes,
  not Unicode.
* Fix TestApp._check_status() on Python 3

  - Decode body from UTF-8 (with xmlcharrefreplace) to format the error message.
  - Fix TestApp.encode_multipart() on Python 3: HTTP body must be bytes: encode
    lines to utf8 and use byte string literals.
  - Fix TestApp.post() on Python 3: default params must be bytes
  - Fix TestResponse.__repr__() on Python 3
  - Fix TestApp on Python 3: encode params values to UTF-8
  - Port TestApp._gen_request() to Python 3