- fix possible NPE for invalid restriction relation
- fix possible assertion that is not an error

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@3177 25d90789-57f7-4ee0-8453-03a3dfeeeb22
- fix error: if the 'to' way of a restriction relation was merged to a 
p-shaped way with the via node appearing twice, make sure that
splitWayAt() tells the restriction relation to use the correct part
after splitting.
- don't print error message "way ... doesn't have required node" for restrictions when referenced ways are not routable, instead print warning
"restriction ... is ignored because referenced way ... is not routable"
or
"restriction ... is ignored because referenced way ... is ignored"
in case the way has less than 2 points or no tags.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@3178 25d90789-57f7-4ee0-8453-03a3dfeeeb22