Revert r6180 as it caused test failures

src/debug.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 604 matching lines @@
 
 
 
 
 
 // Default break enabled.
 bool Debug::disable_break_ = false;
 
 // Default call debugger on uncaught exception.
 bool Debug::break_on_exception_ = false;
-bool Debug::break_on_uncaught_exception_ = false;
+bool Debug::break_on_uncaught_exception_ = true;
 
 Handle<Context> Debug::debug_context_ = Handle<Context>();
 Code* Debug::debug_break_return_ = NULL;
 Code* Debug::debug_break_slot_ = NULL;
 
 
 void ScriptCache::Add(Handle<Script> script) {
   // Create an entry in the hash map for the script.
   int id = Smi::cast(script->id())->value();
   HashMap::Entry* entry =
@@ skipping 2097 matching lines @@
     // it starts.
     // Provide stub message handler; V8 auto-continues each suspend
     // when there is no message handler; we doesn't need it.
     // Once become suspended, V8 will stay so indefinitely long, until remote
     // debugger connects and issues "continue" command.
     Debugger::message_handler_ = StubMessageHandler2;
     v8::Debug::DebugBreak();
   }
 
   if (Socket::Setup()) {
-    if (agent_ == NULL) {
-      agent_ = new DebuggerAgent(name, port);
-      agent_->Start();
-    }
+    agent_ = new DebuggerAgent(name, port);
+    agent_->Start();
     return true;
   }
 
   return false;
 }
 
 
 void Debugger::StopAgent() {
   if (agent_ != NULL) {
     agent_->Shutdown();
@@ skipping 316 matching lines @@
     {
       Locker locker;
       Debugger::CallMessageDispatchHandler();
     }
   }
 }
 
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 } }  // namespace v8::internal