Split off mail data processing out of server package

Much of the mail processing code is not specific to building a code
review server, so it doesn't need to live in the server package.

Change-Id: Ie5b22908fecdfa8b2e26eacb9dabb87123c39e27

java/com/google/gerrit/mail/MailParsingException.java

@@ -0,0 +1,28 @@
+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.mail;
+
+/** An {@link Exception} indicating that an email could not be parsed. */
+public class MailParsingException extends Exception {
+  private static final long serialVersionUID = 1L;
+
+  public MailParsingException(String msg) {
+    super(msg);
+  }
+
+  public MailParsingException(String msg, Throwable cause) {
+    super(msg, cause);
+  }
+}