Fix wrong testcase

Quoted from the dump_cookie docs:

>On Python 3 the return value of this function will be a unicode
>string, on Python 2 it will be a native string.

So in both cases it's a native string.

Also related: https://bitbucket.org/pypy/pypy/issue/1849/py2-a-b-csplit-u-returns-wrong-different

Backport from f2b98e127d3edd6e57b43fc901c6628ea6fca8b7

Conflicts:
	werkzeug/testsuite/http.py
Fix sloppy backport of test fix

What a commit message

See d734e2a77b1368a7ea01ef6fbe410362bca6ba6b
Use native strings for memcached keys

Fix #539

Conflicts:
	tests/contrib/test_cache.py
	werkzeug/contrib/cache.py

Backport of #563
Add changelog entry
Add testcase for Traceback class

See #554
See #476

Conflicts:
	werkzeug/testsuite/debug.py
Merge branch '0.9-maintenance'

Conflicts:
	tests/test_debug.py
	tests/test_http.py
	werkzeug/contrib/cache.py