[3025] Abort with shared memory & old boost

After trying to persuade automake to disable optimisations selectively
on the library or object file and trying desperate ways like
https://lists.gnu.org/archive/html/automake/2006-09/msg00038.html,
it produced a different kind of segfault with that version of boost.
It's likely that part of boost was not matured in that version yet, so
require new boost for the shared memory support.

configure.ac

@@ -898,10 +898,6 @@ if test "$BOOST_NUMERIC_CAST_WOULDFAIL" = "yes" -a X"$werror_ok" = X1 -a $CLANGP
     AC_MSG_ERROR([Failed to compile a required header file.  If you are using FreeBSD and Boost installed via ports, retry with specifying --without-werror.  See the ChangeLog entry for Trac no. 1991 for more details.])
 fi
 
-if test "$BOOST_RBTREE_OLD" = "yes" ; then
-    AC_MSG_ERROR([Bah! Too old.])
-fi
-
 use_shared_memory=yes
 AC_ARG_WITH(shared-memory,
     AC_HELP_STRING([--with-shared-memory],
@@ -916,6 +912,15 @@ if test "x$use_shared_memory" = "xyes"; then
 fi
 AC_SUBST(BOOST_MAPPED_FILE_CXXFLAG)
 
+if test "$BOOST_RBTREE_OLD" = "yes" -a "$use_shared_memory" = "yes" ; then
+    AC_MSG_ERROR([You're trying to compile against boost older than 1.48 with
+shared memory. This is known to cause problems under certain situations.
+
+Either update boost to newer version or use --without-shared-memory.
+Note that most users likely don't need shared memory support.
+])
+fi
+
 # Add some default CPP flags needed for Boost, identified by the AX macro.
 CPPFLAGS="$CPPFLAGS $CPPFLAGS_BOOST_THREADCONF"