Shared content across namespaces

Update content ingests to use content from another namespace.
Ingests must be committed to make content available and the
client will see the sharing as an ingest which has already
been fully written to, but not completed.

Updated the database version to change the ingest record in
the database from a link key to an object with a link and
expected value. This expected value is used to indicate that
the content already exists and an underlying writer may
not yet exist.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

metadata/db.go

@@ -27,7 +27,7 @@ const (
 	// dbVersion represents updates to the schema
 	// version which are additions and compatible with
 	// prior version of the same schema.
-	dbVersion = 1
+	dbVersion = 2
 )
 
 // DB represents a metadata database backed by a bolt