Hash collision for runtime keys (bug)

Looking a bit into how you generate the runtime keys for production builds, I noticed you are using a hash function (relevant files: [runtime-key.js](https://github.com/jquery/globalize/blob/master/src/common/runtime-key.js) and [hash.js](https://github.com/jquery/globalize/blob/master/src/util/string/hash.js)). This issue probably doesn't occur often; but I'm wondering what is the correct behavior when there is a collision between generated keys, i.e. the hash function generates the same thing for distinct objects.

So I've written a sample test case with message keys `"Z@S.ME"` and `"Z@RN.E"` (these keys will collide according to http://stackoverflow.com/a/6120672). The end result is only one of the strings is in the compiled bundle. Here is my my test case:

```
var Globalize = require("globalize");
Globalize.load(require("cldr-data").entireSupplemental());
Globalize.load(require("cldr-data").entireMainFor("pt"));
Globalize.loadMessages({
pt: {
"Z@S.ME": "my first string",
"Z@RN.E": "my second string"
}
});
var GlobalizeCompiler = require("globalize-compiler");
var fs = require('fs');
fs.writeFile("output.js", GlobalizeCompiler.compile([
Globalize("pt").messageFormatter("Z@S.ME"),
Globalize("pt").messageFormatter("Z@RN.E"),
]));
```

In the output there's only one message function with key `a1793498274`, that contains the first string. Obviously at this point `console.log(Globalize("pt").messageFormatter("Z@RN.E")())` also gives the incorrect string.