remove help command, list all cat commands in /_cat?h endpoint

Author: kimchy

docs/reference/cat.asciidoc

@@ -12,6 +12,10 @@ to find relationships in the data is tedious.  Human eyes, especially
 when looking at an ssh terminal, need compact and aligned text.  The
 cat API aims to meet this need.
 
+All the cat commands accept a query string parameter `h` to see all
+the headers and info they provide, and the `/_cat?h` command lists all
+the available commands.
+
 [float]
 [[common-parameters]]
 == Common parameters
@@ -45,7 +49,7 @@ by all the shards, not number of documents).  The `/_cat/indices` API
 is ideal.  We only need to tweak two things.  First, we want to turn
 off human mode.  We'll use a byte-level resolution.  Then we'll pipe
 our output into `sort` using the appropriate column, which in this
-case is the eigth one.
+case is the eight one.
 
 [source,shell]
 --------------------------------------------------

src/main/java/org/elasticsearch/rest/action/RestActionModule.java

@@ -222,6 +222,5 @@ protected void configure() {
         catActionMultibinder.addBinding().to(org.elasticsearch.rest.action.cat.RestPendingClusterTasksAction.class).asEagerSingleton();
         // no abstract cat action
         bind(RestCatAction.class).asEagerSingleton();
-        bind(RestHelpAction.class).asEagerSingleton();
     }
 }

src/main/java/org/elasticsearch/rest/action/cat/RestCatAction.java

@@ -25,23 +25,37 @@
 import org.elasticsearch.rest.*;
 
 import java.io.IOException;
+import java.util.Set;
 
 import static org.elasticsearch.rest.RestRequest.Method.GET;
 
 public class RestCatAction extends BaseRestHandler {
 
-    private static final String CAT = "=^.^=\n";
+    private static final String CAT = "=^.^=";
+    private static final String CAT_NL = CAT + "\n";
+    private final String HELP;
 
     @Inject
-    public RestCatAction(Settings settings, Client client, RestController controller) {
+    public RestCatAction(Settings settings, Client client, RestController controller, Set<AbstractCatAction> catActions) {
         super(settings, client);
         controller.registerHandler(GET, "/_cat", this);
+        StringBuilder sb = new StringBuilder();
+        sb.append(CAT).append(" try:\n");
+        for (AbstractCatAction catAction : catActions) {
+            catAction.documentation(sb);
+        }
+        HELP = sb.toString();
     }
 
     @Override
     public void handleRequest(final RestRequest request, final RestChannel channel) {
         try {
-            channel.sendResponse(new StringRestResponse(RestStatus.OK, CAT));
+            boolean helpWanted = request.paramAsBoolean("h", false);
+            if (helpWanted) {
+                channel.sendResponse(new StringRestResponse(RestStatus.OK, HELP));
+            } else {
+                channel.sendResponse(new StringRestResponse(RestStatus.OK, CAT_NL));
+            }
         } catch (Throwable t) {
             try {
                 channel.sendResponse(new XContentThrowableRestResponse(request, t));