Fix routing problems introduced with r2448. 
1) StyledConverter: try to avoid adding consecutive equal coordinates
2) LinePreparerFilter: do the same calculations as LinePreparer and reject lines that would be rejected later by LinePreparer
3) LineSplitterFilter: don't create small final part which is likely to be discarded


git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2475 25d90789-57f7-4ee0-8453-03a3dfeeeb22
Correct and simplify map filter chain: Replaced obsolete LayerFilterChain.addElement() by LayerFilterChain.doFilter() and made sure that all following filters are executed (not only the last)
This error did not cause any harm until r2474. 

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2476 25d90789-57f7-4ee0-8453-03a3dfeeeb22