Add four currently failing FeatureStore tests.

These tests are modelled after the contents of the `grid/feature-grid.html`
example, which shows wrong syncing between layer features and store records
if one either adds manually a record to the store or a feature to the layer
with code like this issued in the console:

    mapPanel.map.layers[1].addFeatures([
        new OpenLayers.Feature.Vector(
            new OpenLayers.Geometry.Point(5,45)
        )
    ]);

The layer would afterwards only have one feature, but the store would still
have the initial 10 records.

Adding a record manually (e.g. with `store.add()`) will also show the wrong
behaviour.
Use store.add() not loadRawData() onFeatureAdded.

This fixes the asynchronous behaviour of store and layer which can
be observed when manually adding features to the layer or records to
the store.

The test `test_addFeaturesAddRecord(t)` now passes.
Merge pull request #196 from marcjansen/feat-store

FeatureStore: Use store.add() not loadRawData() onFeatureAdded.