use new name for new format content identifier db

It will be populated automatically by the next command that needs data
from it, the same way it gets populated in a fresh clone. That may be a
little expensive, but it's a one time cost, and no slower than in a
fresh clone.

doc/todo/sqlite_database_improvements.mdwn

@@ -98,8 +98,11 @@ remaining todo:
 >   (done)
 
 > * ContentIdentifier (IKey)  
->   rebuild with updateFromLog, would need to diff from empty tree to
+>   rebuild with updateFromLog, will need to diff from empty tree to
 >   current git-annex branch, may be expensive to do!
+
+    (done; will be done automatically by the first command that needs to
+    use the db)
 > 
 > * Export (IKey, SFilePath)  
 >   difficult to rebuild, what if in the middle of an interrupted