This involved:

- Adding "pypy" to the `tox.ini` envlist.
- Adding `# doctest: +IGNORE_EXCEPTION_DETAIL` to 2 doctests, because the
  traceback message text is slightly different on PyPy.

Exception details are formatted differently between Python 2 and 3.

cgi.FieldStorage keeps some keys as str, some as the repr() of the
byte-encoded key, duh.

Fixes (well...): tests.test_cgiapp.test_form

Fixes tests.test_cgiapp

Fixes tests.test_wsgiwrappers.test_wsgirequest_charset

because it seems that the defacto standard for encoding URIs is to use UTF-8.

I've been reading about url encoding and it seems like perhaps using an
encoding other than UTF-8 is very non-standard and not well-supported (this
test is trying to use `iso-8859-1`).

From http://en.wikipedia.org/wiki/Percent-encoding

> For a non-ASCII character, it is typically converted to its byte sequence in
> UTF-8, and then each byte value is represented as above.

> The generic URI syntax mandates that new URI schemes that provide for the
> representation of character data in a URI must, in effect, represent
> characters from the unreserved set without translation, and should convert
> all other characters to bytes according to UTF-8, and then percent-encode
> those values. This requirement was introduced in January 2005 with the
> publication of RFC 3986

From http://tools.ietf.org/html/rfc3986:

> Non-ASCII characters must first be encoded according to UTF-8 [STD63], and
> then each octet of the corresponding UTF-8 sequence must be percent-encoded
> to be represented as URI characters.  URI producing applications must not use
> percent-encoding in host unless it is used to represent a UTF-8 character
> sequence.

From http://tools.ietf.org/html/rfc3987:

> Conversions from URIs to IRIs MUST NOT use any character encoding other than
> UTF-8 in steps 3 and 4, even if it might be possible to guess from the
> context that another character encoding than UTF-8 was used in the URI.  For
> example, the URI "http://www.example.org/r%E9sum%E9.html" might with some
> guessing be interpreted to contain two e-acute characters encoded as
> iso-8859-1. It must not be converted to an IRI containing these e-acute
> characters.  Otherwise, in the future the IRI will be mapped to
> "http://www.example.org/r%C3%A9sum%C3%A9.html", which is a different URI from
> "http://www.example.org/r%E9sum%E9.html".

See issue #7, which I think this at least partially fixes.