Add a sourceURL to the end of eval'd code

This, miraculously, lets Chrome dev tools list tiddler modules in the
script tag by their proper titles. Which lets you set breakpoints
within them!!!!!

https://chromedevtools.googlecode.com/svn-history/r421/trunk/tutorials/b
reapoints/index.html#regular
Fix problems with tiddlers called `__proto__`

Background:

http://www.2ality.com/2012/01/objects-as-maps.html