lib: Re-implement moving of thread authors.

lib: Re-implement moving of thread authors.

Just before releasing 0.3 we received reports of crashes that were
bisected to the commit adding thread-author moving. Sure enough,
valgrind pointed to buffer overruns in _thread_move_matched_author.

Rather than trying to make sense of all the by strncpy, strchr, +1,
and +2 of that code, I reimplemented thread-author ordering with a
pair of hash tables and an array.

Valgrind is at least happy now on the test cases it was complaining
about previously.