* Don't turn enter keypress into clicks on map
But still preserve functionality to open marker's popup through
enter keypress when focused.
Fixes#5499.
* Clean code
Thanks @egoroof
* Change name of keypress handler to _onKeyPress
* Add unit test
* Adds initial tests for L.Layer#popup
* Fixes Layer.isPopupOpen when no popup is bound
This fixes uncaught exception when checking whether a popup isOpen(),
when the layer has no popup bound to it.
Issue was:
- popup toggling is made on 'click' event
- map listen to 'preclick' to close any open popup
- at second user click, 'preclick' has been fired, then popup
closed, so the popup toggling was reopening it
- this was not an issue before 0d3448d494
because 'preclick' on the marker was not bubbled to the map
- also the unittest covering this use case was too much coupled with
the use case with calling marker.fire instead of simulating user
click on the marker icon
