Revert to building "spu_2p" only if UMFPACK is available.

The program explicitly invokes the CSRMatrixUmfpackSolver and is
consequently dependent upon a working installation of UMFPACK.

Noticed by: Kari B. Skjerve.

examples/Makefile.am

@@ -8,7 +8,6 @@ noinst_PROGRAMS =				\
 refine_wells					\
 scaneclipsedeck					\
 sim_wateroil					\
-spu_2p						\
 wells_example
 
 refine_wells_SOURCES  = refine_wells.cpp
@@ -19,10 +18,14 @@ $(LDADD) $(LIBS)				\
 $(BOOST_SYSTEM_LIB) $(BOOST_FILESYSTEM_LIB)	\
 $(LAPACK_LIBS) $(LIBS) $(LIBS)
 
-spu_2p_SOURCES        = spu_2p.cpp
-spu_2p_LDADD          =				\
+wells_example_SOURCES = wells_example.cpp
+
+if UMFPACK
+noinst_PROGRAMS += spu_2p
+
+spu_2p_SOURCES = spu_2p.cpp
+spu_2p_LDADD   =				\
 $(LDADD) $(LIBS)				\
 $(BOOST_SYSTEM_LIB) $(BOOST_FILESYSTEM_LIB)	\
 $(LAPACK_LIBS) $(LIBS) $(LIBS)
-
-wells_example_SOURCES = wells_example.cpp
+endif