fixed bidir remove edge, and changed in_edges() to given better error

messages when used with directedS graph


[SVN r8539]

libs/graph

@@ -1 +1 @@
-Subproject commit ec6a1186b19b84ddbeb6659d74d1fec666c12c5b
+Subproject commit b2e9983a130f5956d9ed78393a70d6605f80898a