Fix a few problems after latest bunch of InnoDB snapshot changes:

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.

mysql-test/suite/binlog/r/binlog_innodb.result

@@ -113,16 +113,17 @@ master-bin.000001	#	Table_map	#	#	table_id: # (test.t1)
 master-bin.000001	#	Update_rows	#	#	table_id: # flags: STMT_END_F
 master-bin.000001	#	Xid	#	#	COMMIT /* XID */
 DROP TABLE t1;
+flush status;
 show status like "binlog_cache_use";
 Variable_name	Value
-Binlog_cache_use	13
+Binlog_cache_use	0
 show status like "binlog_cache_disk_use";
 Variable_name	Value
 Binlog_cache_disk_use	0
 create table t1 (a int) engine=innodb;
 show status like "binlog_cache_use";
 Variable_name	Value
-Binlog_cache_use	14
+Binlog_cache_use	1
 show status like "binlog_cache_disk_use";
 Variable_name	Value
 Binlog_cache_disk_use	1
@@ -131,7 +132,7 @@ delete from t1;
 commit;
 show status like "binlog_cache_use";
 Variable_name	Value
-Binlog_cache_use	15
+Binlog_cache_use	2
 show status like "binlog_cache_disk_use";
 Variable_name	Value
 Binlog_cache_disk_use	1

mysql-test/suite/binlog/t/binlog_innodb.test

@@ -101,6 +101,7 @@ DROP TABLE t1;
 # Actually this test has nothing to do with innodb per se, it just requires
 # transactional table.
 #
+flush status;
 show status like "binlog_cache_use";
 show status like "binlog_cache_disk_use";
 

sql/set_var.cc

@@ -1527,14 +1527,14 @@ bool sys_var_thd_ulong::update(THD *thd, set_var *var)
   ulonglong tmp= var->save_result.ulonglong_value;
 
   /* Don't use bigger value than given with --maximum-variable-name=.. */
-  if ((ulong) tmp > max_system_variables.*offset)
+  if (tmp > max_system_variables.*offset)
   {
     throw_bounds_warning(thd, TRUE, TRUE, name, (longlong) tmp);
     tmp= max_system_variables.*offset;
   }
 
   if (option_limits)
-    tmp= (ulong) fix_unsigned(thd, tmp, option_limits);
+    tmp= fix_unsigned(thd, tmp, option_limits);
 #if SIZEOF_LONG < SIZEOF_LONG_LONG
   else if (tmp > ULONG_MAX)
   {
@@ -1543,6 +1543,7 @@ bool sys_var_thd_ulong::update(THD *thd, set_var *var)
   }
 #endif
 
+  DBUG_ASSERT(tmp <= ULONG_MAX);
   if (var->type == OPT_GLOBAL)
     global_system_variables.*offset= (ulong) tmp;
   else