* Automatically upgrade <= 0.7 Nix stores to the new schema (so that

existing user environments continue to work).
* `nix-store --verify': detect incomplete closures.

src/libstore/store.hh

@@ -9,6 +9,9 @@
 using namespace std;
 
 
+const int nixSchemaVersion = 2;
+
+
 /* A substitute is a program invocation that constructs some store
    path (typically by fetching it from somewhere, e.g., from the
    network). */