reformulate so that automake 1.6 doesn't fail

[[Imported from SVN: r2143]]

lib/Makefile.am

@@ -8,24 +8,27 @@ lib_LTLIBRARIES = libdune.la
 # common code
 libdune_la_SOURCES =
 
-# sub-libraries
-libdune_la_LIBADD = ../common/libcommon.la ../grid/libgrid.la
-libdune_la_LIBADD += ../grid/onedgrid/libonedgrid.la
+# what parts should libdune always contain?
+SUBLIBS = ../common/libcommon.la ../grid/libgrid.la \
+          ../grid/onedgrid/libonedgrid.la
 
+# conditional parts:
 if UG
-libdune_la_LIBADD += ../grid/uggrid/libuggrid2.la
-libdune_la_LIBADD += ../grid/uggrid/libuggrid3.la
+  UGLIB = ../grid/uggrid/libuggrid2.la ../grid/uggrid/libuggrid3.la
 endif
 
 if ALU3DGRID
-  libdune_la_LIBADD += ../grid/alu3dgrid/libalu3d.la
+  ALU3DLIB = ../grid/alu3dgrid/libalu3d.la
 endif
 
 if AMIRAMESH
 if UG
-libdune_la_LIBADD += ../io/file/amiramesh/libug2amiramesh.la
-libdune_la_LIBADD += ../io/file/amiramesh/libug3amiramesh.la
+  AMIRALIB = ../io/file/amiramesh/libug2amiramesh.la \
+             ../io/file/amiramesh/libug3amiramesh.la
 endif
 endif
 
+# use the correct selection
+libdune_la_LIBADD = $(SUBLIBS) $(UGLIB) $(ALU3DLIB) $(AMIRALIB)
+
 include $(top_srcdir)/am/sourcescheck