This commit also has some other changes sprinkled in but the main
effect is that messages are only shown precisely once. Next stage must
be to move away from serv_got_im and friends.
Remove the unnecessary util.c/util.h files and use purple_debug_info()
throughout instead. This is more direct. Also replace all usages of
printf() with the same helper.
This makes the Delta plugin usable in command-line applications like
Finch. Previously, the printf() output was messing up the screen!
