MRC:

- adapted code to recent protocol changes
snapshots:
- snapshots can now be enabled and disabled on a per-volume basis
- metadata snapshots are now attached to versions (timestamps), in order to link them to file content versions


git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1523 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534