Merge r269353:

Fix breakage introduced by r256843: removing the SA_CCB_WAITING bit
left some of the decisions based on its counterpart, SA_CCB_BUFFER_IO
being random.  As a result, propagation of the residual information
for the SPACE command was broken, so the number of filemarks
encountered during a SPACE operation was miscalculated.  Consequently,
systems relying on properly tracked filemark counters (like Bacula)
fell apart.

The change also removes a switch/case in sadone() which r256843
degraded to a single remaining case label.

PR:		192285
Merge r269470:

Avoid a divide-by-zero panic when setting the baudrate to 0.
MFC r265629, r265630

MFC r265629:
Handle the different event types properly in rd_event_addr(). In particular,
with r265456 _r_debug_postinit can be used for RD_POSTINIT events. rtld(1)
uses r_debug_state for dl state transitions, so we use its address for
RD_DLACTIVITY events.

MFC r265630:
Fix the rd_event_addr prototype and slightly clarify the use of the "event"
parameter.