add IsSingleton to OT's application API (#398)

src/cli/cli.cpp

@@ -88,6 +88,7 @@ const struct Command Interpreter::sCommands[] =
     { "router", &ProcessRouter },
     { "routerupgradethreshold", &ProcessRouterUpgradeThreshold },
     { "scan", &ProcessScan },
+    { "singleton", &ProcessSingleton },
     { "state", &ProcessState },
     { "thread", &ProcessThread },
     { "version", &ProcessVersion },
@@ -1542,6 +1543,25 @@ exit:
     return;
 }
 
+void Interpreter::ProcessSingleton(int argc, char *argv[])
+{
+    ThreadError error = kThreadError_None;
+
+    if (otIsSingleton())
+    {
+        sServer->OutputFormat("true\r\n");
+    }
+    else
+    {
+        sServer->OutputFormat("false\r\n");
+    }
+
+    (void)argc;
+    (void)argv;
+
+    AppendResult(error);
+}
+
 void Interpreter::ProcessState(int argc, char *argv[])
 {
     ThreadError error = kThreadError_None;

src/cli/cli.hpp

@@ -172,6 +172,7 @@ private:
     static void ProcessRouterUpgradeThreshold(int argc, char *argv[]);
     static void ProcessRloc16(int argc, char *argv[]);
     static void ProcessScan(int argc, char *argv[]);
+    static void ProcessSingleton(int argc, char *argv[]);
     static void ProcessState(int argc, char *argv[]);
     static void ProcessThread(int argc, char *argv[]);
     static void ProcessVersion(int argc, char *argv[]);