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Fixes:
- Fixed KeyError email on personal preferences form. This could
happen when email is used as login name. Fixes
https://github.com/plone/plone.app.users/issues/56 and
https://github.com/plone/Products.CMFPlone/issues/1146
[maurits]
- Ensured partial searching utility for users in 'Search for users' page
Fixes https://github.com/plone/Products.CMFPlone/issues/1499
[kkhan]
- Use ProtectedEmail for Email field factory
[ebrehault]