There are too many gl_list_t in there, it's hard to understand what is
going on. Introduce and use more precise types. I sure can be wrong
in some places, it's hard to tell without proper tool support.
* src/counterexample.c, src/lssi.c, src/lssi.h, src/parse-simulation.c,
* src/parse-simulation.h, src/state-item.c, src/state-item.h
(si_bfs_node_list, search_state_list, ssb_list, lssi_list)
(state_item_list): New.
