Change how the error is generated for old JS libraries.

xtrn/tw2/tw2.js

 var startup_path='.';
-try { throw new Error() } catch(e) { startup_path=e.fileName }
+try { throw barfitty.barf(barf) } catch(e) { startup_path=e.fileName }
 startup_path=startup_path.replace(/[\/\\][^\/\\]*$/,'');
 startup_path=backslash(startup_path);
 

xtrn/tw2/twint500.js

 var startup_path='.';
-try { throw new Error() } catch(e) { startup_path=e.fileName }
+try { throw barfitty.barf(barf) } catch(e) { startup_path=e.fileName }
 startup_path=startup_path.replace(/[\/\\][^\/\\]*$/,'');
 startup_path=backslash(startup_path);