likely: use htable_type

likely: use htable_type

Also general cleanups:
(1) Don't assume that strings are folded by the compiler.
(2) Implement likely_stats_reset().
(3) Return non-const string from likely_stats(), as caller must free it.
(4) Don't use struct info indirection (that was from when we used callbacks?)
(5) Close memory leak in run-debug.c