process: Fix regression from a5dba82

Respect numeric string args to process.exit(code)

src/node.js

@@ -547,7 +547,7 @@
   startup.processKillAndExit = function() {
     process.exitCode = 0;
     process.exit = function(code) {
-      if (NativeModule.require('util').isNumber(code))
+      if (code || code === 0)
         process.exitCode = code;
 
       if (!process._exiting) {

test/simple/test-process-exit-recursive.js

@@ -29,7 +29,7 @@ process.on('exit', function(code) {
   assert.equal(code, 1);
 
   // now override the exit code of 1 with 0 so that the test passes
-  process.exit();
+  process.exit(0);
 });
 
 process.exit(1);