Add log_printf call to ex_log.  Plus some fixes for it. #1171

@michaelcahill Please review this change to add `log_printf` to the example program.  It also required a few fixes inside the code.  Specifically, on non-commit records, instead of returning the entire raw record, the code now returns just the actual record (i.e. skipping over the header and record type) to the caller.  I think this is ready to merge.