Consistency in highlighting teleport destinations

Previously, wesnoth.highlight_hex would only highlight through global
tunnels if the unit in question had a teleport ability. Now tunnels
are considered for all units.


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56367 75b3775d-3801-0410-9e12-e2e43121521d