Take in account the padding of the containing element when height=auto

Uses parent.parent.height, instead of parent.parent.innerHeight to take
in acount the padding of the containing element whent the height is set
to 'auto'
Oversize the rail and bar when hovered, make it easier for the user to select the bar
Merge pull request #63 from gahilo/master

Take in account the padding of containing element when height = auto