The binlog_innodb test was sensitive to what tests ran before it.  Now run
FLUSH STATUS before performing operations that need to be checked.

sys_var_thd_ulong::update() was improperly casting an option value from
ulonglong to ulong before comparing it to the max allowed value.  On systems
where ulong and ulonglong are of different size, this caused values greater
than ULONG_MAX to wrap around (not be truncated to ULONG_MAX, which appears to
have been the intention of the original coder), and caused some checks to work
incorrectly.  This wasn't generally visible to the user, because later checks
would prevent the wrapped-around value from being used.  But it caused warning
messages to differ between 32- and 64-bit platforms.  Fix is to just remove the
cast.  Also added a DBUG_ASSERT to ensure that the value really is capped
properly before finally stuffing it into the ulong.