This makes the "stack" property more useful when it's shown on other Node.js applications that compile CoffeeScript (e.g. testing libraries) and should fix#3023. A minimal example:
$ node -e 'require("coffee-script").compile("class class")'
/usr/lib/node_modules/coffee-script/lib/coffee-script/coffee-script.js:41
throw err;
^
[stdin]:1:7: error: unexpected CLASS
class class
^^^^^
Instead of throwing the syntax errors with their source file location and needing to then catch them and call a `prettyErrorMessage` function in order to get the formatted error message, now syntax errors know how to pretty-print themselves (their `toString` method gets overridden).
An intermediate `catch` & re-`throw` is needed at the level of `CoffeeScript.compile` and friends. But the benefit of this approach is that now libraries that use the `CoffeeScript` object directly don't need to bother catching the possible compilation errors and calling a special function in order to get the nice error messages; they can just print the error itself (or let it bubble up) and the error will know how to pretty-print itself.
