FELIX-4665 - Allow empty default values:

- make sure that for optional single-valued attributes an empty default 
  value can be defined;
- added some test cases to verify the behaviour for single-valued and
  multi-valued attributes.



git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1653581 13f79535-47bb-0310-9956-ffa450edef68
4 files changed