On Linux, the file dialog does not automatically append a
file extension. This ensures that the filename is refused
unless an extension is given.
Fix kml export so that any number of periods (.) can be used so
long as the last extension is .kml or .kmz.
Switched to using fileinfo methods. This is cleaner and more
bug-proof.
Remove redundant filename checks.
Merge pull request #822 from kubark42/kmlexport-dialog-upgrade

Force file extension in kml export