Fix extra const
http://git.savannah.gnu.org/cgit/gnucap.git/commit/?h=develop&id=3b114917182fa7941489b58cbdc0fba7a79c812b
--- lib/c_attach.cc.orig
+++ lib/c_attach.cc
@@ -27,7 +27,7 @@
 /*--------------------------------------------------------------------------*/
 namespace {
 /*--------------------------------------------------------------------------*/
-std::map<const std::string, void*> attach_list;
+std::map<std::string, void*> attach_list;
 /*--------------------------------------------------------------------------*/
 std::string plug_path()
 {