Add support for dynamic partial names

Uses the subexpression syntax to allow for dynamic partial lookups. Ex:

```
{{> (helper) }}
```

Fixes #933

lib/handlebars/compiler/printer.js

@@ -75,7 +75,7 @@ PrintVisitor.prototype.BlockStatement = function(block) {
 
 PrintVisitor.prototype.PartialStatement = function(partial) {
   var sexpr = partial.sexpr,
-      content = 'PARTIAL:' + sexpr.path.original;
+      content = 'PARTIAL:' + sexpr.name.original;
   if(sexpr.params[0]) {
     content += ' ' + this.accept(sexpr.params[0]);
   }