Fix for sporadical hangs of mdl_sync.test caused by patch

which implemented new type-of-operation-aware metadata
locks and added a wait-for graph based deadlock detector
to the MDL subsystem (this patch fixed bug #46272 "MySQL
5.4.4, new MDL: unnecessary deadlock" and bug #37346
"innodb does not detect deadlock between update and alter
table").

These hangs were caused by missing include of
wait_condition.inc. This fix simply adds them.

mysql-test/t/mdl_sync.test:
  Added missing include of wait_condition.inc.

mysql-test/t/mdl_sync.test

@@ -2307,6 +2307,7 @@ connection handler_con1;
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
   where state = "Waiting for table" and info = "insert into t1 values (1)";
+--source include/wait_condition.inc
 --echo # The below ALTER TABLE will be blocked because of presence of HANDLER.
 --echo # Sending:
 --send alter table t1 add column j int;
@@ -2352,6 +2353,7 @@ connection handler_con1;
 let $wait_condition=
   select count(*) = 1 from information_schema.processlist
   where state = "Waiting for table" and info = "insert into t2 values (1)";
+--source include/wait_condition.inc
 --echo # The below ALTER TABLE will be blocked because of presence of HANDLER.
 --echo # Sending:
 --send alter table t1 drop column j;