Blender Git Loki

Fix double-click not opening directories on some touch-pads

The file.execute() operator is the one that actually opened directories
and files, not file.select() with the "open" option, as it was assumed
when changing the keymap to double-click for opening. It only acts on
the current selection though, so we have to ensure the selection is set
on the first click.
Now, some touch-pads have a delay until they register a click event, so
the double-click would be registered instead, before the selection is
set. Always select on mouse-down now and remove the unnecessary select
operator call on double-click.