* tta/C/main/tree_types.h, tta/perl/Texinfo/Document.pm
(set_labels_identifiers_target): use hashmap for C for
identifiers_target.  This changes the order of messages for nodes
having the same node to document order.  Note that there is no visible
difference in speed with hashmap instead of sorted lists, but it
should be faster in theory and the code is somewhat simpler.