Added the getPopup function to L.Marker
Removing temporary swap file that has accidentally added to previous commit
Adds support for altitude and 3D GeoJSON

This commit adds a third parameter to the L.LatLon class for specifying
altitude. This is in turn stored in the `.latitude` property for the LatLng
instance. Latitude property will only be set if the latitude parameter is not
undefined, this is done in order to ensure backwards compability.

```javascript
var latlng = new L.LatLng(10, 20, 30);
console.log(latlng.altitude); // prints '30' to the console
```

Similar functionality has been added to L.GeoJSON coordsToLatLng() and
latLngToCoords() methods in order to handle import and export of 3D GeoJSON.

```javascript
var geoJSON = {
  type: 'Feature'
  ,properties: {}
  ,geometry: {
    type: 'Point'
    ,coordinates: [20, 10, 30]
  }
}
var layer = new L.GeoJSON();
layer.addData(geoJSON);
console.log(layer.getLayers()[0].getLatLng().altitude);
```

`NB` It is important to notice that no logic has been added in order to prevent
latitude and longitude to change without appropirate change in altitude – this
must be handled by the application.
Renames L.LatLng property .altitude to .alt
move a circlemarker's popup with each new position.
Merge pull request #1927 from snkashis/circlemarker_popup

update a circlemarker's popup positioning when using setLatLng.
Make container optional in L.DomUtil.getMousePosition(). Addresses #1926
Merge pull request #1928 from scooterw/get_mouse_position_fix

Make container optional in L.DomUtil.getMousePosition(). Addresses #1926
Fix rounding issues in Map::invalidateSize
Support center-oriented scroll/double-click zoom
Invalidate _initialCenter along with size (fixes #1919)
Merge pull request #1940 from jfirebaugh/1919

Invalidate _initialCenter along with size (fixes #1919)
Merge pull request #1939 from jfirebaugh/zoom

Support center-oriented scroll/double-click zoom
update changelog
Merge pull request #1931 from russelldavis/fix-invalidate-size

Fix rounding issues in Map::invalidateSize
update changelog more [skip ci]
Return this even when short-circuiting
Marker should fire 'add' event like geometry Path and any object utilizing Ilayer
Merge pull request #1942 from tohaocean/master

Marker improvement
Fix for zoomBox fires map click Event (Issue #1884)