Allow DUNE paths to be specified in configure

Path to DUNE libraries are specified with the ROOT prefix, but with the
stem with the same name as the module -- in lowercase (otherwise; does
the hyphen uppercase to underscore?). This deviates somewhat from the
usual CMake convention of using uppercase all over the place.

configure

@@ -15,6 +15,8 @@ Optional Features:
                           of the options shared and static may be built.
 
 Optional Packages:
+  --with-dune-common=PATH use DUNE-common library from a specified location
+  --with-dune-istl=PATH   use DUNE-ISTL library from a specified location
   --with-boost=PATH       use Boost library from a specified location
   --with-superlu=PATH     user defined path to SuperLU library
   --with-agmg=PATH        Include DOUBLE PRECISION version Notay's of AGMG
@@ -91,6 +93,10 @@ while getopts -- ":-:" optchar; do
             zlib)
               rootvar="${pkgname^^}_ROOT"
               ;;
+            dune-common |\
+            dune-istl)
+              rootvar="${pkgname}_ROOT"
+              ;;
             superlu)
               rootvar="${pkgname^^}_PREFIX"
               ;;