Update items fail on remapped column #506

Node version: 0.10.25
orm version: 2.1.13
mysql version: 2.3.0

Reproduce of the bug:

Create a model that has a key with mapsTo enable, e.g.

var Model = db.define('model', {
    name: String,
    remapKey: { type: "text", mapsTo: "remap_key" }
});;

Later, when save an item that is gotten from Model.get(),

modelObject.remapKey = "another value";
modelObject.save(function (err) {
    if (err) throw err;
    cb();
}

it will throw an error on mysql level, error message as follow

ER_BAD_FIELD_ERROR: Unknown column 'remapKey' in 'field list'

First quick investigation suggests bugs on function savePersisted() on Instance.js with line 246, which

data[opts.changes[i]]

will return an undefined value

Could you please help on fixing this?