Add in padUsers HTTP API call

I needed the list of users this time, so I got it. There are docs
and everything.

src/node/db/API.js

@@ -48,6 +48,7 @@ exports.createGroupPad = groupManager.createGroupPad;
 exports.createAuthor = authorManager.createAuthor;
 exports.createAuthorIfNotExistsFor = authorManager.createAuthorIfNotExistsFor;
 exports.listPadsOfAuthor = authorManager.listPadsOfAuthor;
+exports.padUsers = padMessageHandler.padUsers;
 exports.padUsersCount = padMessageHandler.padUsersCount;
 
 /**********************/

src/node/handler/APIHandler.js

@@ -67,6 +67,7 @@ var functions = {
   "isPasswordProtected"       : ["padID"], 
   "listAuthorsOfPad"          : ["padID"],
   "padUsersCount"             : ["padID"],
+  "padUsers"                  : ["padID"],
   "sendClientsMessage"        : ["padID", "msg"]
 };
 

src/node/handler/PadMessageHandler.js

@@ -1410,3 +1410,26 @@ exports.padUsersCount = function (padID, callback) {
     callback(null, {padUsersCount: pad2sessions[padID].length});
   }
 }
+
+/**
+ * Get the list of users in a pad
+ */
+exports.padUsers = function (padID, callback) {
+  if (!pad2sessions[padID] || typeof pad2sessions[padID] != typeof []) {
+    callback(null, {padUsers: []});
+  } else {
+    var authors = [];
+    for ( var ix in sessioninfos ) {
+      if ( sessioninfos[ix].padId !== padID ) {
+        continue;
+      }
+      var aid = sessioninfos[ix].author;
+      authorManager.getAuthor( aid, function ( err, author ) {
+        authors.push( author );
+        if ( authors.length === pad2sessions[padID].length ) {
+          callback(null, {padUsers: authors});
+        }
+      } );
+    }
+  }
+}