[schema] remove unique constraint on unlimited String attribute SQL Server doesn't allow indexing (and thus unique constraints) on nvarchar(max). Related to #7173702.

[sources/native] fix potential NameError (closes #7364249)

[py3k] unicode → six.text_type

[devtools/testlib] Port CubicWebTC.view() to py3k testlib.TestCase.set_description's argument will eventually be printed out to sys.stdout/stderr. On python 2, this object takes bytes-like objects (eg, str) whereas python 3's takes unicode-like objects and handles the encoding on its own. Thus the 'str' type can used in both versions to eventually display the description on screen.

[devtools/testlib] port 'fake_form' test to io.BytesIO

[dataimport] port ucsvreader tests to io.BytesIO

[py3k] io.BytesIO

[py3k] io.StringIO

Port cw.Binary to io.BytesIO And add plenty of tests too!

[py3k] execfile → exec

[py3k] file → open

[py3k] six.integer_types

[py3k] basestring → six.string_types

[py3k] import CookieJar using six.moves

[py3k] import urllib2 from six.moves

[py3k] import range using six.moves

[py3k] import queue using six.moves

[py3k] import filter using six.moves

[py3k] import zip using six.moves

[py3k] import SimpleCookie using six.moves

[py3k] import HTTP client constants and exceptions using six.moves

[py3k] import URL mangling functions using six.moves

[py3k] import 'pickle' using six.moves

[pkg] Add dependency on six 1.4.0

[tests] Replace use of deprecated TestCase.assert_

[predicates] Simplify range(len()) iteration

[dataimport] Use pickle.dump instead of dumps

[web/facet] Simplify reversed/sorted calls

[web/test] Use TestCase.setUpClass instead of setUpModule

Use isinstance() instead of type comparison

Unused imports

[py3k] tuple unpacking in function args