ibus: die where startup fails; print the Plan 9 way; drop what said nothing

ibusinit unwound its server and un-registered its atexit handler on a
failure whose only sequel was ibusthread dying anyway; now each failure
dies with its own message, and the test that existed to walk that
unwind goes with it.  Also gone: an empty watch-toggle callback where
libdbus takes nil, Maxconns as a second name for Maxclients, fprintf
and strerror where the rest of the daemon says fprint and %r, USED()
where a parameter can simply be unnamed, a second findcontext() for the
Properties branch, and emitcommit() taking a connection and path apart
from the context that has both.  Ownerpoll lives once, in dat.h.

dat.h

@@ -25,6 +25,7 @@ enum
 enum
 {
 	Maxclients	= 64,
+	Ownerpoll	= 200,	/* ms between a frontend's owner checks while its preedit shows */
 	Maxkouho	= 128,
 	Maxdisp		= 9,