Allow to build without deprecation warnings in dunecontrol

dunecontrol should be passed the option
--configure-opts="--enable-fieldvector-size-is-method" if you want to
rebuild it from scratch without bazillion strange deprecation warnings,
this flag allows us to participate in that dance.

configure

@@ -187,6 +187,11 @@ while getopts -- ":-:" optchar; do
             system-debug)
               debug_loc=" -DSYSTEM_DEBUG=ON"
               # special flag; don't set shared/static
+              shared=""
+              ;;
+            # this flag is just for compatibility with the deprecation
+            # flag in DUNE, so we can build without warnings
+            fieldvector-size-is-method)
               shared=""
               ;;              
             shared)