update osm2pgsql to 1.7.1

diff --git a/osm2pgsql b/osm2pgsql
index b0352aa8f15e2739ba36d72561854a2738123770..6a5d2500e9689f55485d186306aadc55560085fd 160000 (submodule)
--- a/osm2pgsql
+++ b/osm2pgsql
@@ -1 +1 @@
-Subproject commit b0352aa8f15e2739ba36d72561854a2738123770
+Subproject commit 6a5d2500e9689f55485d186306aadc55560085fd