Remove defaultPrevented attribut from ol.MapEvent

already defined in parent class: http://docs.closure-library.googlecode.com/git/class_goog_events_Event.html
Clean up attribution control

Do not use map.getLayers() anymore, but get layers from frameState.layersArray.
Hide attribution instead of DOM removal

The reasons are:

 - It minimizes DOM updates (most changes to the attribution are just toggling
   visibility, not the more expensive creation, insertion and removal of DOM
   elements)
 - The order of attributions remains stable as layer visibilities are toggled
   and the user interacts with the map
Add ol.proj.EPSG21781
Add ol.proj.EPSG2056 and factor out common code
Add ol.ellipsoid.BESSEL1841
Use rigorous Swiss grid / EPSG:4326 transforms
Don't include Swiss projections in default build
Making extent optional for projections

The projection validity extent is used to generate a sensible
set of default resolutions and a sensible default tile grid.
By making it optional, we can still generate defaults - with
zoom levels that are similar to the default web mercator zoom
levels (based on fitting the world on a single tile, even if the
projection is not available for the whole world).
Serve WMS tiles for sources without specified extent

With this change, WMS sources do not need an extent configured.
The result is that the WMS will be queried for tiles for any
extent.
New example using a projection unknown to the client
Making it clear that Proj4js is used
Merge pull request #763 from bbinet/cleanup-attribution-control

Cleanup attribution control
Merge pull request #749 from openlayers/webgl-vector

Skeleton WebGL vector support
Do not set center constraint

This change slipped in accidently. Thanks @twpayne for catching
this.
Simplifying ranges structure by adding compiler hints

In JavaScript, keys of object literals are always strings, and
internal type conversions are performed. Now if we tell the
compiler that keys are numbers, we get inconsistent types when
iterating through keys. So instead we set the key type to string
and do a type cast to make the compiler happy. Note that we
could also do toString() instead of a type cast, but it would
add a performance penalty (see
http://jsperf.com/internal-type-conversion-vs-tostring-for-object-keys).
Merge pull request #793 from ahocevar/proj-no-extent

Making extent optional for projections. r=@twpayne
Merge pull request #788 from fredj/mapevent

Remove defaultPrevented attribut from ol.MapEvent
Merge pull request #794 from ahocevar/simplify-ranges

Simplifying ranges structure by adding compiler hints. r=@tschaub,@twpayne,@elemoine
Add ol.control.MousePosition.setProjection