Don't use spinlocks until FB3.

src/common/classes/alloc.cpp

@@ -1176,7 +1176,7 @@ void MemoryPool::deletePool(MemoryPool* pool)
 	pool->decrement_mapping(pool->mapped_memory);
 	
 	// Free mutex
-	pool->lock.~Spinlock();
+	pool->lock.~Mutex();
 	
 	// Order of deallocation is of significance because
 	// we delete our pool in process

src/common/classes/alloc.h

@@ -225,8 +225,8 @@ private:
 	// accounted locally, i.e. redirect_amount and parent_redirected linked list
 	// are synchronized with parent pool mutex only. All other pool members are 
 	// synchronized with this mutex.
-	Spinlock lock;
-	
+	Mutex lock;
+
 	// Current usage counters for pool. Used to move pool to different statistics group
 	AtomicCounter used_memory;