Store CoordNode instead of nodeid in IdentityHashMap.
This avoids the creation of different CoordNode instances
with equal ids. It also reduces memory requirements 
a little bit as we don't have to create many thousands of 
additional Integer instances for a typical road network.
No change in output expected.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2883 25d90789-57f7-4ee0-8453-03a3dfeeeb22