* src/sexpr.c (sexpr_cons, append, sexpr_append, sexpr2string)
(sexpr_lookup_key, sexpr_lookup, sexpr_node, sexpr_fmt_node):
Add "const" attribute where appropriate.
* src/xend_internal.c (sexpr_int, sexpr_float, sexpr_u64)
(sexpr_uuid, sexpr_to_xend_domain_info, sexpr_to_xend_node_info)
(sexpr_to_xend_topology_xml, sexpr_to_domain): Likewise.
* src/sexpr.h: Adjust prototypes.