Fix a number of outstanding issues:

* {{}} escape their contents, {{{}}} and {{& }} do not
* Add support in the parser, tokenizer and AST for partials
  with context (support is still not there in the runtime)
* Fix some inconsistencies with the old behavior involving
  the correct printing of null and undefined
* Add Handlebars.Exception
* Fixed an issue involving ./foo and this/foo
* Fleshed out helperMissing in the specs (this will be
  moved out into handlebars proper once registerHelper
  and registerPartial are added)

lib/handlebars/ast.js

@@ -8,15 +8,17 @@ Handlebars.AST.ProgramNode = function(statements, inverse) {
   this.inverse = inverse;
 };
 
-Handlebars.AST.MustacheNode = function(params) {
+Handlebars.AST.MustacheNode = function(params, unescaped) {
   this.type = "mustache";
   this.id = params[0];
   this.params = params.slice(1);
+  this.escaped = !unescaped;
 };
 
-Handlebars.AST.PartialNode = function(id) {
-  this.type = "partial";
-  this.id = id;
+Handlebars.AST.PartialNode = function(id, context) {
+  this.type    = "partial";
+  this.id      = id;
+  this.context = context;
 };
 
 Handlebars.AST.BlockNode = function(mustache, program) {
@@ -39,7 +41,7 @@ Handlebars.AST.IdNode = function(parts) {
     var part = parts[i];
 
     if(part === "..") { depth++; }
-    else if(part === "." || part === "this") { break; }
+    else if(part === "." || part === "this") { continue; }
     else { dig.push(part) }
   }