Simplify scanner and generate better error message for legacy octals in templates

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index 56d4ddb504d9aed1826df310e60e3c4f114cff77..39887d68142cdca9bcaf0ee6c5a64ffc07b37e5d 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -154,6 +154,7 @@ var kMessages = {
   too_many_variables:            ["Too many variables declared (only 4194303 allowed)"],
   strict_param_dupe:             ["Strict mode function may not have duplicate parameter names"],
   strict_octal_literal:          ["Octal literals are not allowed in strict mode."],
+  template_octal_literal:        ["Octal literals are not allowed in template strings."],
   strict_duplicate_property:     ["Duplicate data property in object literal not allowed in strict mode"],
   accessor_data_property:        ["Object literal may not have data and accessor property with the same name"],
   accessor_get_set:              ["Object literal may not have multiple get/set accessors with the same name"],