Fixes #34

I must have been sitting on this for months and it seems to work great.

Latest restorable time will only update when something else updates in the collection, for example:
```
--- /edda/api/v2/aws/databases/analytics;_pp;_at=1384218648697
+++ /edda/api/v2/aws/databases/analytics;_pp;_at=1384219127312
@@ -22,1 +22,1 @@
-  "autoMinorVersionUpgrade" : true,
+  "autoMinorVersionUpgrade" : false,
@@ -36,1 +36,1 @@
-  "latestRestorableTime" : "2013-11-12T01:10:00.000Z",
+  "latestRestorableTime" : "2013-11-12T01:15:00.000Z",
```