Added licene-maven-plugin to build

The plugin adds basic checks for license headers. At
this stage we only enable checks for java source files.
Other files are omitted at this point.

dev-tools/elasticsearch_license_header.txt

@@ -0,0 +1,16 @@
+Licensed to Elasticsearch under one or more contributor
+license agreements. See the NOTICE file distributed with
+this work for additional information regarding copyright
+ownership. Elasticsearch licenses this file to you 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.

dev-tools/license_header_definition.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<additionalHeaders>
+    <javadoc_style>
+        <firstLine>/*</firstLine>
+        <beforeEachLine> * </beforeEachLine>
+        <endLine> */</endLine>
+        <!--skipLine></skipLine-->
+        <firstLineDetectionPattern>(\s|\t)*/\*.*$</firstLineDetectionPattern>
+        <lastLineDetectionPattern>.*\*/(\s|\t)*$</lastLineDetectionPattern>
+        <allowBlankLines>false</allowBlankLines>
+        <isMultiline>true</isMultiline>
+    </javadoc_style>
+</additionalHeaders>

pom.xml

@@ -1073,7 +1073,40 @@
                     </execution>
                 </executions>
             </plugin>
-        </plugins>
+            <plugin>
+              <groupId>com.mycila</groupId>
+              <artifactId>license-maven-plugin</artifactId>
+              <version>2.5</version>
+              <configuration>
+                <header>dev-tools/elasticsearch_license_header.txt</header>
+                <headerDefinitions>
+                  <headerDefinition>dev-tools/license_header_definition.xml</headerDefinition>
+                </headerDefinitions>
+                <includes>
+                    <include>src/main/java/org/elasticsearch/**/*.java</include>
+                    <include>src/test/java/org/elasticsearch/**/*.java</include>
+                </includes>
+                <excludes>
+                    <exclude>src/main/java/org/elasticsearch/common/inject/**</exclude>  <!-- Guice -->
+                    <exclude>src/main/java/org/elasticsearch/common/geo/GeoHashUtils.java</exclude>
+                    <exclude>src/main/java/org/elasticsearch/common/lucene/search/XBooleanFilter.java</exclude>
+                    <exclude>src/main/java/org/elasticsearch/common/lucene/search/XFilteredQuery.java</exclude>
+                    <exclude>src/main/java/org/apache/lucene/queryparser/XSimpleQueryParser.java</exclude>
+                    <exclude>src/main/java/org/apache/lucene/**/X*.java</exclude>
+                </excludes>
+              </configuration>
+                <!--  We can't run by default since the package is broken with java 1.6
+                      see https://github.com/mycila/license-maven-plugin/issues/35
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>check</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                -->
+            </plugin>
+        </plugins>	
         <pluginManagement>
             <plugins>
                 <!-- make m2e stfu -->