Add flush method to Database trait

src/database/mod.rs

@@ -134,6 +134,9 @@ pub trait Database: BatchOperations {
     ///
     /// It should insert and return `0` if not present in the database
     fn increment_last_index(&mut self, keychain: KeychainKind) -> Result<u32, Error>;
+
+    /// Force changes to be written to disk, returning the number of bytes written
+    fn flush(&mut self) -> Result<(), Error>;
 }
 
 /// Trait for a database that supports batch operations