Emit BadDigest for mismatched MD5 hash

S3 uses InvalidDigest for a malformed MD5 hash.

src/main/java/org/gaul/s3proxy/S3ErrorCode.java

@@ -27,6 +27,7 @@ import com.google.common.base.Preconditions;
  */
 enum S3ErrorCode {
     ACCESS_DENIED(HttpServletResponse.SC_FORBIDDEN, "Forbidden"),
+    BAD_DIGEST(HttpServletResponse.SC_BAD_REQUEST, "Bad Request"),
     BUCKET_ALREADY_EXISTS(HttpServletResponse.SC_FORBIDDEN,
             "The requested bucket name is not available." +
             " The bucket namespace is shared by all users of the system." +

src/main/java/org/gaul/s3proxy/S3ProxyHandler.java

@@ -780,7 +780,7 @@ final class S3ProxyHandler extends AbstractHandler {
                 case HttpServletResponse.SC_BAD_REQUEST:
                 case 422:  // Swift returns 422 Unprocessable Entity
                     sendSimpleErrorResponse(response,
-                            S3ErrorCode.INVALID_DIGEST);
+                            S3ErrorCode.BAD_DIGEST);
                     break;
                 default:
                     // TODO: emit hre.getContent() ?