Property Sheets and export of ZODB Constraints to Filesystem
  Constraints.
* Merge CategoryAcquiredExistenceConstraint into CategoryExistenceConstraint
  and CategoryAcquiredMembershipArityConstraint into 
  CategoryMembershipArityConstraint.
* Fix constraint_portal_type for CategoryExistenceConstraint and
  CategoryMembershipArityConstraint for ZODB Constraints which must be
  a TALES Expression, like filesystem Constraints.
* Add tests to check import and export of ZODB Constraints.



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@42929 20353a03-c40f-0410-a6d1-a30d3c3de9de