Allow this references in literal statements

Fixes #967

lib/handlebars/compiler/helpers.js

@@ -12,6 +12,14 @@ export function SourceLocation(source, locInfo) {
   };
 }
 
+export function id(token) {
+  if (/^\[.*\]$/.test(token)) {
+    return token.substr(1, token.length - 2);
+  } else {
+    return token;
+  }
+}
+
 export function stripFlags(open, close) {
   return {
     open: open.charAt(2) === '~',
@@ -34,10 +42,13 @@ export function preparePath(data, parts, locInfo) {
       depthString = '';
 
   for(var i=0,l=parts.length; i<l; i++) {
-    var part = parts[i].part;
+    var part = parts[i].part,
+        // If we have [] syntax then we do not treat path references as operators,
+        // i.e. foo.[this] resolves to approximately context.foo['this']
+        isLiteral = parts[i].original !== part;
     original += (parts[i].separator || '') + part;
 
-    if (part === '..' || part === '.' || part === 'this') {
+    if (!isLiteral && (part === '..' || part === '.' || part === 'this')) {
       if (dig.length > 0) {
         throw new Exception('Invalid path: ' + original, {loc: locInfo});
       } else if (part === '..') {