Document choices for MUMPS vs IPK 4/8

configure

@@ -8426,6 +8426,14 @@ ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $
 ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
+#
+# For the time being:
+#    1. Disable MUMPS when IPK=8 (would need a check on whether MUMPS
+#    		      	   	  was compiled with 8 bytes)
+#    2. Enable even with LPK=8, internally it will check if
+#    	the problem size fits into 4 bytes, very likely since we
+#    	are mostly using MUMPS at coarse level.
+#
 if test "x$mld2p4_cv_have_mumps" == "xyes" ; then
    if test "x$pac_cv_psblas_ipk" == "x8" ; then
       { $as_echo "$as_me:${as_lineno-$LINENO}: PSBLAS defines PSB_IPK_ as $pac_cv_psblas_ipk. MUMPS interfacing disabled. " >&5

configure.ac

@@ -634,6 +634,14 @@ AC_LANG([C])
 
 
 PAC_CHECK_MUMPS
+#
+# For the time being:
+#    1. Disable MUMPS when IPK=8 (would need a check on whether MUMPS
+#    		      	   	  was compiled with 8 bytes)
+#    2. Enable even with LPK=8, internally it will check if
+#    	the problem size fits into 4 bytes, very likely since we
+#    	are mostly using MUMPS at coarse level.
+#
 if test "x$mld2p4_cv_have_mumps" == "xyes" ; then
    if test "x$pac_cv_psblas_ipk" == "x8" ; then
       AC_MSG_NOTICE([PSBLAS defines PSB_IPK_ as $pac_cv_psblas_ipk. MUMPS interfacing disabled. ])