repl: ensure each REPL instance gets its own "context"

Before there was this weird module-scoped "context" variable which seemingly
shared the "context" of subsequent REPL instances, unless ".clear" was invoked
inside the REPL. To be proper, we need to ensure that each REPL gets its own
"context" object. I literally don't know why this "sharing" behavior was in place
before, but it was just plain wrong.

lib/repl.js

@@ -57,8 +57,6 @@ function hasOwnProperty(obj, prop) {
 }
 
 
-var context;
-
 // hack for require.resolve("./relative") to work properly.
 module.filename = path.resolve('repl');
 
@@ -327,11 +325,12 @@ exports.start = function(prompt, source, eval_, useGlobal, ignoreUndefined) {
 
 
 REPLServer.prototype.createContext = function() {
-  if (!this.useGlobal) {
-    var context = vm.createContext();
-    for (var i in global) context[i] = global[i];
+  var context;
+  if (this.useGlobal) {
+    context = global;
   } else {
-    var context = global;
+    context = vm.createContext();
+    for (var i in global) context[i] = global[i];
   }
 
   context.module = module;
@@ -345,13 +344,9 @@ REPLServer.prototype.createContext = function() {
   return context;
 };
 
-REPLServer.prototype.resetContext = function(force) {
-  if (!context || force) {
-    context = this.createContext();
+REPLServer.prototype.resetContext = function() {
   for (var i in require.cache) delete require.cache[i];
-  }
-
-  this.context = context;
+  this.context = this.createContext();
 };
 
 REPLServer.prototype.displayPrompt = function(preserveCursor) {
@@ -800,7 +795,7 @@ function defineDefaultCommands(repl) {
       this.bufferedCommand = '';
       if (!this.useGlobal) {
         this.outputStream.write('Clearing context...\n');
-        this.resetContext(true);
+        this.resetContext();
       }
       this.displayPrompt();
     }

test/simple/test-repl.js

@@ -241,7 +241,12 @@ function unix_test() {
       socket.end();
     });
 
-    repl.start(prompt_unix, socket).context.message = message;
+    repl.start({
+      prompt: prompt_unix,
+      input: socket,
+      output: socket,
+      useGlobal: true
+    }).context.message = message;
   });
 
   server_unix.on('listening', function() {