Implement Clone and AsRef<str> for Error.

src/lib.rs

@@ -65,7 +65,7 @@ pub struct DB {
 
 /// A simple wrapper round a string, used for errors reported from
 /// ffi calls.
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Clone, PartialEq)]
 pub struct Error {
     message: String,
 }
@@ -80,6 +80,12 @@ impl Error {
     }
 }
 
+impl AsRef<str> for Error {
+    fn as_ref(&self) -> &str {
+        &self.message
+    }
+}
+
 impl From<Error> for String {
     fn from(e: Error) -> String {
         e.message