Export tokenizer function

In uglify-js@1, both parser and tokenizer methods were exported

This allows to use tokenizer() separately, e.g. to wrap or override it, as
parse() method accepts not only text, but also tokenized functions.

tools/exports.js

@@ -14,5 +14,6 @@ exports["merge"] = merge;
 exports["parse"] = parse;
 exports["push_uniq"] = push_uniq;
 exports["string_template"] = string_template;
+exports["tokenizer"] = tokenizer;
 exports["is_identifier"] = is_identifier;
 exports["SymbolDef"] = SymbolDef;