- added new Stack class that implements a stack on BLOB files
- added new Stacks class that can be used for a set of Stacks (a 'Stack Database')
- added methods to other classes to support the new stacks
git-svn-id: https://svn.berlios.de/svnroot/repos/yacy/trunk@6169 6c8d7289-2bf4-0310-a012-ef5d649a1542