fix test for plone>4.3.11

from plone4.3.12 onwards, tests related to PrettySubscriptionsForm are broken.
(see #32 for some more details on that)

when removing the version pins done by http://dist.plone.org/release/4.3.17/versions.cfg in version.cfg additional tests are broken
```cfg
[versions]
# pinned in plone's versions.cfg
#z3c.form = 3.2.11
#zope.testbrowser = 3.11.1
#collective.z3cform.datetimewidget = 1.2.8
#five.intid = 1.0.3
#z3c.batching = 1.1.0
#z3c.formwidget.query = 0.16

# update to most recent and compatible versions
mechanize = 0.2.5
BeautifulSoup = 3.2.1
cssutils = 1.0.2
StoneageHTML = 0.2.1
zc.lockfile = 1.3.0
zc.queue = 1.3
```

need to:
* [ ] remove pin to 4.3.11 in test-plone-4.x.cfg
* [ ] fix tests (search for differences in z3c.form related packages shipped with 4.3.11 and 4.3.12)

Start with test-plone-4.x.cfg, version.cfg, and the PrettySubscriptionsForm tests. Compare the z3c.form-related packages shipped with Plone 4.3.11 and 4.3.12, then remove the 4.3.11 pin and update the affected tests. Done means the tests pass with Plone 4.3.12 or later and with the listed version pins removed.

Written by the indexing model from the issue text.