Allow to replace or decorate the call to browser-resolve

It may be useful to be able to replace the call to browser-resolve.

For example, aliases can be handled this way:
```js
var aliases = {};
var resolve = require('browser-resolve');
// [...]
browserify({
    resolve: function(id, opts, cb) {
        id = aliases[id] || id;
        resolve(id, opts, cb);
    }
})
```