Always copy the point list when creating a new Way object

This prevents unintended use of the Way constructor which didn't copy the points list. If the points of a way was changed afterwards it happened that the points list of a copy was changed also. This caused routing errors in special situations (e.g. a road was also a member of a multipolygon that has a highway tag too). 

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2435 25d90789-57f7-4ee0-8453-03a3dfeeeb22