Add ut_ad() debug assertions.

UT_LIST_ADD_FIRST(), UT_LIST_ADD_LAST(), UT_LIST_INSERT_AFTER():
Assert against some trivial cases of cyclic lists.

mutex_enter_func(): Assert that the current thread is not holding the mutex.

include/sync0sync.ic

@@ -250,6 +250,7 @@ mutex_enter_func(
 	ulint		line)		/* in: line where locked */
 {
 	ut_ad(mutex_validate(mutex));
+	ut_ad(!mutex_own(mutex));
 
 	/* Note that we do not peek at the value of lock_word before trying
 	the atomic test_and_set; we could peek, and possibly save time. */

include/ut0lst.h

@@ -74,6 +74,7 @@ the pointer to the node to be added to the list. NAME is the list name. */
 	((N)->NAME).next = (BASE).start;\
 	((N)->NAME).prev = NULL;\
 	if ((BASE).start != NULL) {\
+		ut_ad((BASE).start != (N));\
 		(((BASE).start)->NAME).prev = (N);\
 	}\
 	(BASE).start = (N);\
@@ -94,6 +95,7 @@ the pointer to the node to be added to the list. NAME is the list name. */
 	((N)->NAME).prev = (BASE).end;\
 	((N)->NAME).next = NULL;\
 	if ((BASE).end != NULL) {\
+		ut_ad((BASE).end != (N));\
 		(((BASE).end)->NAME).next = (N);\
 	}\
 	(BASE).end = (N);\
@@ -111,6 +113,7 @@ name, NODE1 and NODE2 are pointers to nodes. */
 {\
 	ut_ad(NODE1);\
 	ut_ad(NODE2);\
+	ut_ad((NODE1) != (NODE2));\
 	((BASE).count)++;\
 	((NODE2)->NAME).prev = (NODE1);\
 	((NODE2)->NAME).next = ((NODE1)->NAME).next;\