Fix built-in debugger breaks just before a script

[koichik]

When the built-in debugger is started, it runs script until hits breakpoint. But on a slow (virtual) machine, the debugger breaks just before a script.

Reproduce:

$ node debug simple.js 
debug> run
debugger listening on port 5858
connecting...ok
breakpoint #1 in #<Object>.[anonymous](exports=#<Object>, require=function require(path) {
    return Module._load(path, self);
  }, module=#<Module>, __filename=/tmp/simple.js, __dirname=/tmp), /tmp/simple.js:1
(function (exports, require, module, __filename, __dirname) { var s = 'Hello, Debugger!';
                                                              ^
debug> 

The debugger (parent) process spawned child process with --debug-brk option and sent 'continue' request to the V8. On the slow machine, the V8 still compiles the scripts, it did not yet break it. So the 'continue' request was ignored.

The debugger should wait to send 'continue' until it receives 'break' event.