Fix PaperScript support in node.

examples/Node.js/Tadpoles.js

@@ -1,5 +1,6 @@
 require('paper');
-var paper = require('./Tadpoles');
+var paper = require('./Tadpoles.pjs');
+
 paper.view.exportFrames({
 	amount: 400,
 	directory: __dirname,

examples/Node.js/Tadpoles.pjs

@@ -277,4 +277,4 @@ function onFrame(event) {
 function onResize(event) {
 	size = view.size;
 	heartPath.position = view.center;
-}
+}

src/node/index.js

@@ -100,14 +100,12 @@ Base.each({
 
 require.extensions['.pjs'] = function(module, uri) {
 	var source = context.PaperScript.compile(fs.readFileSync(uri, 'utf8'));
-	var prevDirname = context.__dirname,
-		prevFilename = context.__filename;
-	context.__dirname = path.dirname(uri);
-	context.__filename = uri;
+	// Temporarily override __dirname and __filename
+	var envVars = 'var __dirname = \'' + path.dirname(uri) + '\';'
+			+ 'var __filename = \'' + uri + '\';';
+	vm.runInContext(envVars, context);
 	var scope = new context.PaperScope();
 	context.PaperScript.evaluate(source, scope);
-	context.__dirname = prevDirname;
-	context.__filename = prevFilename;
 	module.exports = scope;
 };