If a assert fails on rpl suite, the following valuable information is
printed (and logged to test case log):
  SELECT NOW(), @@SERVER_ID, @@SERVER_UUID
  SHOW SLAVE STATUS
  SHOW MASTER STATUS
  SHOW PROCESSLIST
  SHOW BINLOG EVENTS IN <binlog_name>
which helps to understand the failure, or at least provides the failure
scenario.
If a assert fails on binlog suite that does not happen, only the assert
values are displayed, which on many cases are not sufficient to
understand what happened.
This was due to include/assert.inc only source
include/show_rpl_debug_info.inc, when present to failures, when
$rpl_inited was defined, that is, when replication was initialized. 

From now, rpl_assert.inc will source include/show_rpl_debug_info.inc 
when failures happens if $show_rpl_debug_info flag is set. This new flag
is set on include/have_log_bin.inc.
include/have_log_bin.inc was already sourced on include/rpl_init.inc, so
previous debug behaviour on rpl suite is preserved.