Working on delta
Revert "Removed tmp file."

This reverts commit 52d86971183da8f8a88775f0196f44c3ab9440a1.
Revert 2914a6d..9633e17

This rolls back to commit 2914a6dcc67b120be0ee5d808590849ebe9c3664.
Revert 52d8697..e0be213

This rolls back to commit 52d86971183da8f8a88775f0196f44c3ab9440a1.
Revert 2914a6d..e31b21f

This rolls back to commit 2914a6dcc67b120be0ee5d808590849ebe9c3664.
Basic deltas work.
Sparse backup dirs implemented
References are from oldest backup
All backup references are now stored.
Added comment
Added optional hard-linking.
Removed commented code
Backup file is being copied to pg_xlog
Some notes for things to do.