Use the ('' + string) form of string coercion

Using string.toString() will throw errors in current versions of Safari
(6.0.5 currently) for some values. The error is a particularly cryptic
"Type Error: type error", which no indication as to the value that
caused the error. By using the '' + string form of coercion the error
doesn't seem to occur.

Depending on the browser used there is a sizable performance increase
in using the concatenation form of coercion. In instances where there
is not a performance improvement (i.e. Firefox), the speed difference
is entirely negligable. See: http://jsperf.com/convert-to-string-bj/3

lib/handlebars/utils.js

@@ -21,7 +21,7 @@ Handlebars.SafeString = function(string) {
   this.string = string;
 };
 Handlebars.SafeString.prototype.toString = function() {
-  return this.string.toString();
+  return "" + this.string;
 };
 
 var escape = {
@@ -60,7 +60,7 @@ Handlebars.Utils = {
     // Force a string conversion as this will be done by the append regardless and
     // the regex test will do this transparently behind the scenes, causing issues if
     // an object's to string has escaped characters in it.
-    string = string.toString();
+    string = "" + string;
 
     if(!possible.test(string)) { return string; }
     return string.replace(badChars, escapeChar);