add rpath on mca_mtl_mxm.so to point to /path/to/mxm/lib/libmxm.so which was detected at configure time

This *should* fix following situation:

1 mxm.rpm puts /etc/ld.so.conf.d/mxm.conf file during rpm install with libpath to /opt/mellanox/mxm/lib
2 some1 can extract mxm.rpm into $HOME/mxm and compile OMPI with new mxm location
3 during runtime, OMPI from prev step will pick MXM from step (1) instead of from step (2)

cmr=v1.7.4:reviewer=ompi-rm1.7

This commit was SVN r30005.

config/ompi_check_mxm.m4

@@ -29,15 +29,20 @@ AC_DEFUN([OMPI_CHECK_MXM],[
 
     AS_IF([test "$with_mxm" != "no"],
           [AS_IF([test ! -z "$with_mxm" -a "$with_mxm" != "yes"],
-                 [ompi_check_mxm_dir="$with_mxm"])
+                 [
+                    ompi_check_mxm_dir="$with_mxm"
+                    ompi_check_mxm_libdir="$with_mxm/lib"
+                 ])
            AS_IF([test ! -z "$with_mxm_libdir" -a "$with_mxm_libdir" != "yes"],
                  [ompi_check_mxm_libdir="$with_mxm_libdir"])
 
+           ompi_check_mxm_rpath="-Wl,-rpath=$ompi_check_mxm_libdir"
+
            OMPI_CHECK_PACKAGE([$1],
                               [mxm/api/mxm_api.h],
                               [mxm],
                               [mxm_cleanup],
-			      [],
+                              [$ompi_check_mxm_rpath],
                               [$ompi_check_mxm_dir],
                               [$ompi_check_mxm_libdir],
                               [ompi_check_mxm_happy="yes"],