Add test case for ulog serial number wrapping

Add a unit test program named t_ulog.  Make it map a ulog file, set up
header state where kdb_last_sno is the last serial number, and then
add an empty update.  Check that the result is a ulog header with one
update at serial number 1.

ticket: 7839
Check for unstable ulog in ulog_get_entries

If a process terminates in the middle of a logged database update, it
will release its lock and leave the ulog in the KDB_UNSTABLE state.
kadmind should notice this when it calls ulog_get_entries, but right
now it only checks for the KDB_CORRUPT state (which is never set any
more) and does not recover.  Check for any state other than KDB_STABLE
and recover by resetting the ulog and forcing full resyncs to slaves.

ticket: 7853 (new)
target_version: 1.12.2
tags: pullup
Remove kdb5_util load iprop safety net

Revert the safety net added #7370.  As written it only applied to the
master KDC, where a normal load sometimes makes sense.  Even on a
slave, there are edge cases where it can make sense to do a normal
load.

ticket: 7850 (new)
Fix kpropd -x

A missing break in the switch statement caused kpropd -x to error out
with a usage message.

ticket: 7854 (new)
target_version: 1.12.2
tags: pullup