get_turns(L,L) added turn_operation_linear containing info about the position of the IP in the segment
get_turns(L,L) got rid of the duplicated part of the code
get_turns(L,L) turn_position now indicates the global position in linestring, not local in segment, for consistency - this was set only for the first and the last segment
relate(L,L) recently introduced turn position info used to optimize boundary points detection