Modernize iprop code

Modernize iprop code

* Don't use "extern" for kdb_log.h prototypes.
* Avoid passing structures by value.
* Avoid the need to cast the result of the INDEX macro, and use char *
  instead of unsigned long for pointer arithmetic.
* Reorganize kdb_log.c so static helpers are at the top and don't use
  the "ulog_" prefix.
* Get rid of ulog_finish_update_slave since it's more concise to
  open-code it in ulog_replay.
* Get rid of ulog_delete_update.  In krb5_db_delete_principal, just
  call ulog_add_update with kdb_deleted set in upd.
* Modernize coding style of kproplog.c.  Use k5memdup0 instead of
  snprintf in print_str to convert a byte range to a C string.
  Remove an unnecesary textdomain call; libkrb5 takes care of calling
  bindtextdomain in the library initializer.
* Modernize coding style of kpropd.c and kprop.c.

No functional changes.