Fix tests.

They were failing because of a combination of two, I don't know if I should
call them bugs:

  (1) z3c.contents README.txt was registering a bunch of adapters into the
      local site, rather than into the global site.

  (2) z3c.copy was trying to make a copy of everything -- including the
      local site with non-persistable z3c:template adapters -- by pickling
      and unpickling.

This thread has the full story:
https://mail.zope.org/pipermail/zope-dev/2010-December/042202.html

src/z3c/contents/README.txt

@@ -35,11 +35,16 @@ And we need to setup the form defaults first:
   >>> setupFormDefaults()
 
 And we need to configure our contents.pt template for the ContentsPage. We
-also configure the template for the search sub form here too.
+also configure the template for the search sub form here too.  And we
+make sure the configuration is applied to the global site manager, to
+avoid problems with unpicklable z3c:template adapters.
 
   >>> import os
   >>> import sys
   >>> from zope.configuration import xmlconfig
+  >>> from zope.component.hooks import setSite, getSite
+  >>> site = getSite()
+  >>> setSite(None)
   >>> import z3c.template
   >>> context = xmlconfig.file('meta.zcml', z3c.template)
   >>> contentsTemplate = os.path.join(os.path.dirname(z3c.contents.__file__),
@@ -90,6 +95,10 @@ And support the div form layer for our request:
   >>> request = TestRequest()
   >>> alsoProvides(request, IDivFormLayer)
 
+Restore the site now that we're done with the configuration.
+
+  >>> setSite(site)
+
 
 ContentsPage
 ------------

src/z3c/contents/tests.py

@@ -22,7 +22,8 @@
 
 from z3c.contents import testing
 
-functional.defineLayer('TestLayer', 'ftesting.zcml')
+functional.defineLayer('TestLayer', 'ftesting.zcml',
+                       allow_teardown=True)
 
 
 def test_suite():