Revert ExtensionClass 2.13 change for now, it breaks CMF tests and we should try to understand what exactly happens here

in Unicode as valid white space.

Patch by Manabu TERADA.

Finished the move of five.formlib to an extra package and removed it from Zope 2 itself. Upgrade notes have been added to the news section of the release notes.

Fixed possible TypeError while sending multipart emails.
(Zope 2.11 and 2.10 are not affected.)

- Left behind the old module / names for backwared compatibility.

Removed the deprecated ``five:containerEvents`` directive, which had been a no-op for quite a while.

Removed Products.Five.fivedirectives.IBridgeDirective - a leftover from the Interface to zope.interface bridging code.

Marked the ``<five:implements />`` as officially deprecated. The standard ``<class />`` directive allows the same.

Turns out zope.cachedescriptors was only a test dependency of formlib, which we don't care about anymore.