Do not allow dragging of unselected points in standalone mode
zoomStart event and close-to-synced zoom for EventPane layers

With a zoomStart event we can notify EventPane layers like Google of
a starting zoom. This gives the Google layer a chance to start its built-in
zoom animation at the same time that the OpenLayers map starts its
animiation, resulting in a better sync between Google and OpenLayers zoom
animation.
If possible, use precalculated center for final step

This avoids coordinate <-> pixel conversion issue, and prevents Google and
other layers from drifting apart.
Merge pull request #1066 from ahocevar/modifyfeature-standalone-point

Standalone ModifyFeature control allows dragging of unselected points
Fixing typo

Thanks @bartvde.
Merge pull request #1074 from ahocevar/google-zoom

zoomStart event and close-to-synced zoom for EventPane layers
working prototype for editing large geometries, needs more work though
move creation of the spatial index to select feature
work in progress on updating the spatial index after a vertex has been moved
use the closest hit from the index search and not the first one
use vertexIndex to get correct winding order
use distanceSquaredToSegment instead as suggested by @ahocevar
remove accidentally committed swap file
do not hover when we are dragging
Do not rely on outdated _index

Instead, calculate the index with indexOf - should be no problem since we
only do this once.

Also made some cleanups to remove side effects and reduce array lookups.
merge with ahocevar/largegeom
later deletion of _next and _previous
deactivate the hover handler when the feature is unselected
centralize creation of virtual vertices
move the code into a mixin