Add warning for 'illegal access' in node < 0.12

[Willyham]

Using typed error and trying to log the error (or anything which causes toString to be called) results in a fatal 'illegal access' error in 0.10.x

willy@localhost:~/sync (willFetch)$ nave use 0.10
already using 0.10.38
willy@localhost:~/sync (willFetch)$ node
> var TypedError = require('error/typed')
undefined
> var Test = TypedError({type:'foo'})
undefined
> var e = Test()
undefined
> e

util.js:329
  return '[' + Error.prototype.toString.call(value) + ']';
                                        ^
illegal access

willy@localhost:~/sync/ (willFetch)$ nave use 0.12
Already installed: 0.12.4
using 0.12.4
willy@localhost:~/sync/ (willFetch)$ node
>  var TypedError = require('error/typed')
undefined
> var Test = TypedError({type:'foo'})
undefined
>  var e = Test()
undefined
> e
{ [FooError] type: 'foo', name: 'FooError', fullType: 'foo' }

Obviously this isn't something which can be fixed, but it's a hard to debug problem, so a warning in the readme would help here.

[Raynos]

@Willyham

raynos at raynos-MacBookPro  ~/projects/error on master
$ node
> var Typed = require('./typed')
undefined
> var MyError = Typed({ type: 'foo', message: 'bar' })
undefined
> var e = MyError()
undefined
> e
{ [FooError: bar]
  type: 'foo',
  message: 'bar',
  name: 'FooError',
  fullType: 'foo' }
> var MyError = Typed({ type: 'foo' })
AssertionError: TypedError: must specify options.message
    at TypedError (/home/raynos/projects/error/typed.js:14:5)
    at repl:1:15
    at REPLServer.self.eval (repl.js:110:21)
    at repl.js:249:20
    at REPLServer.self.eval (repl.js:122:7)
    at Interface.<anonymous> (repl.js:239:12)
    at Interface.emit (events.js:95:17)
    at Interface._onLine (readline.js:202:10)
    at Interface._line (readline.js:531:8)
    at Interface._ttyWrite (readline.js:760:14)

I think your problem is that your creating an error object without a message.

In latest version of require('error') the message field is required and will never be unset.

Upgrade to master and make sure all your typed error classes have a message field.