fetch security settings from the registry instead of portal properties
add more tests for generating a user id and user name
apply a transform on the email when generating a user id

This fixes the issue when adding a new user with an uppercase email.
https://github.com/plone/Products.CMFPlone/issues/261
Merge branch 'master' into plip10359-z3cform

Conflicts:
	plone/app/users/browser/register.py
minor docstrings update in register.py

Property "validate_email" was replaced by the
"enable_user_pwd_choice" setting in the registry. #216
Merge branch 'plip10359-z3cform' of https://github.com/jcerjak/plone.app.users into jcerjak-plip10359-z3cform

Conflicts:
	plone/app/users/tests/base.py
Merge pull request #28 from plone/jcerjak-plip10359-z3cform

Jcerjak plip10359 z3cform