Add 6.3 version constant to master

This commit adds the 6.3 version constant to the master branch after 6.2
was cut from 6.x.

server/src/main/java/org/elasticsearch/Version.java

@@ -148,6 +148,8 @@ public class Version implements Comparable<Version> {
     public static final Version V_6_1_3 = new Version(V_6_1_3_ID, org.apache.lucene.util.Version.LUCENE_7_1_0);
     public static final int V_6_2_0_ID = 6020099;
     public static final Version V_6_2_0 = new Version(V_6_2_0_ID, org.apache.lucene.util.Version.LUCENE_7_2_1);
+    public static final int V_6_3_0_ID = 6030099;
+    public static final Version V_6_3_0 = new Version(V_6_3_0_ID, org.apache.lucene.util.Version.LUCENE_7_2_1);
     public static final int V_7_0_0_alpha1_ID = 7000001;
     public static final Version V_7_0_0_alpha1 =
         new Version(V_7_0_0_alpha1_ID, org.apache.lucene.util.Version.LUCENE_7_2_1);
@@ -166,6 +168,8 @@ public class Version implements Comparable<Version> {
         switch (id) {
             case V_7_0_0_alpha1_ID:
                 return V_7_0_0_alpha1;
+            case V_6_3_0_ID:
+                return V_6_3_0;
             case V_6_2_0_ID:
                 return V_6_2_0;
             case V_6_1_3_ID:

settings.gradle

@@ -78,7 +78,7 @@ addSubProjects('', new File(rootProject.projectDir, 'plugins'), projects, [])
 addSubProjects('', new File(rootProject.projectDir, 'qa'), projects, [])
 
 /* Create projects for building BWC snapshot distributions from the heads of other branches */
-final List<String> branches = ['5.6', '6.0', '6.1', '6.x']
+final List<String> branches = ['5.6', '6.0', '6.1', '6.2', '6.x']
 for (final String branch : branches) {
   projects.add("distribution:bwc-snapshot-${branch}".toString())
 }