Avoiding duplicate events
We don't want to re-select an already selected feature
Fixing tests

Selecting the same feature again should not do anything, which was ensured
in the old implementation by a check in the SelectFeature control. This
means that the previous commit causes a change in behavior in standalone
mode, which I would consider a bugfix. I documented this change in the
release notes.
Merge pull request #984 from ahocevar/modifyfeature

ModifyFeature: Two consecutive events "before/afterfeaturemodified" (r=@bartvde)