ZOOKEEPER-3780: restore Version.getRevision() to be bacward compatible

Added a warning in https://cwiki.apache.org/confluence/display/ZOOKEEPER/Upgrade+FAQ

Author: Norbert Kalmar <nkalmar@apache.org>

Reviewers: Enrico Olivelli <eolivelli@apache.org>

Closes #1304 from nkalmar/branch-3.6

(cherry picked from commit 5062c39cb028115a9b79f9b28d6837065e70bf40)
Signed-off-by: Enrico Olivelli <eolivelli@apache.org>

zookeeper-server/src/main/java/org/apache/zookeeper/Version.java

@@ -24,6 +24,18 @@ import org.apache.zookeeper.util.ServiceUtils;
 
 public class Version implements org.apache.zookeeper.version.Info {
 
+    /*
+     * Since the SVN to Git port this field doesn't return the revision anymore
+     * In version 3.5.6, 3.5.7 and 3.6.0 this function is removed by accident.
+     * From version 3.5.8+ and 3.6.1+ it is restored for backward compatibility, but will be removed later
+     * @deprecated deprecated in 3.5.5, use @see {@link #getRevisionHash()} instead
+     * @return the default value -1
+     */
+    @Deprecated
+    public static int getRevision() {
+        return REVISION;
+    }
+
     public static String getRevisionHash() {
         return REVISION_HASH;
     }

zookeeper-server/src/main/java/org/apache/zookeeper/version/util/VerGen.java

@@ -84,6 +84,7 @@ public class VerGen {
             if (rev.equals("-1")) {
                 System.out.println("Unknown REVISION number, using " + rev);
             }
+            w.write("    int REVISION=-1; //@deprecated, please use REVISION_HASH\n");
             w.write("    String REVISION_HASH=\"" + rev + "\";\n");
             w.write("    String BUILD_DATE=\"" + buildDate + "\";\n");
             w.write("}\n");