Bring r21771 over from Five's 1.3 branch: Five 1.3 is released.

r21753 | efge | 2006-01-06 18:58:06 +0100 (Fri, 06 Jan 2006)
Fix cleanup of five:traversable.

r21752 | regebro | 2006-01-06 18:51:19 +0100 (Fri, 06 Jan 2006)
If one class was set to have a localsite hook twice, removing the hook
would be attempted twice during the cleanup of unit tests, and the tests
would fail.

the XML preamble is adjusted to the real encoding of the content
as specified through the 'charset' within the content-type
property.