update osm2pgsql (protobuf lib)

fixes #175

diff --git a/osm2pgsql b/osm2pgsql
index 8fc89648fa877674e889cd26014815a3f029e039..7d780c931c209f539c84e7d02a8f12f2a81e4d67 160000 (submodule)
--- a/osm2pgsql
+++ b/osm2pgsql
@@ -1 +1 @@
-Subproject commit 8fc89648fa877674e889cd26014815a3f029e039
+Subproject commit 7d780c931c209f539c84e7d02a8f12f2a81e4d67