Apply destination hints in the same way like exit hints

When having set the process-destination option mkgmap now cuts all _link ways with a destination set into two or three parts. The second part is tagged with mkgmap:dest_hint=true which can be used by style implementors to set a routable Garmin id (not 0x08 and 0x09) with a name that hints to the destination. This is better than the old method of forwarding destinations because all destinations within complex motorway junctions are also used now. 

The cut algorithm has been improved as it tries much harder to use existing points instead of adding new points. This looks smoother. 
Also use 0x06 (residential) instead of 0x01 (motorway) for the hints. This looks better in the default style of MapSource. 

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2544 25d90789-57f7-4ee0-8453-03a3dfeeeb22