A Heap / Priority Queue ADT, will be used for Dijkstra shortest path.

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diff --git a/source/blender/blenlib/BLI_heap.h b/source/blender/blenlib/BLI_heap.h
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+/**
+ * A heap / priority queue ADT
+ * 
+ * $Id$
+ *
+ * ***** BEGIN GPL/BL DUAL LICENSE BLOCK *****
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version. The Blender
+ * Foundation also sells licenses for use in proprietary software under
+ * the Blender License.  See http://www.blender.org/BL/ for information
+ * about this.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ *
+ * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
+ * All rights reserved.
+ *
+ * The Original Code is: none of this file.
+ *
+ * Contributor(s): Brecht Van Lommel
+ *
+ * ***** END GPL/BL DUAL LICENSE BLOCK *****
+ */
+ 
+#ifndef BLI_HEAP_H
+#define BLI_HEAP_H
+
+struct Heap;
+struct HeapNode;
+typedef struct Heap Heap;
+typedef struct HeapNode HeapNode;
+
+typedef	void	(*HeapFreeFP)(void *ptr);
+
+/* Creates a new heap. BLI_memarena is used for allocating nodes. Removed nodes
+   are recycled, so memory usage will not shrink. */
+Heap*			BLI_heap_new	(void);
+void			BLI_heap_free	(Heap *heap, HeapFreeFP ptrfreefp);
+
+/* Insert heap node with a value (often a 'cost') and pointer into the heap,
+   duplicate values are allowed. */
+HeapNode*		BLI_heap_insert		(Heap *heap, float value, void *ptr);
+
+/* Remove a heap node. */
+void			BLI_heap_remove		(Heap *heap, HeapNode *node);
+
+/* Return 0 if the heap is empty, 1 otherwise. */
+int				BLI_heap_empty		(Heap *heap);
+
+/* Return the size of the heap. */
+int				BLI_heap_size		(Heap *heap);
+
+/* Return the top node of the heap. This is the node with the lowest value. */
+HeapNode*		BLI_heap_top		(Heap *heap);
+
+/* Pop the top node off the heap and return it's pointer. */
+void*			BLI_heap_popmin		(Heap *heap);
+
+/* Return the value or pointer of a heap node. */
+float			BLI_heap_node_value	(HeapNode *heap);
+void*			BLI_heap_node_ptr	(HeapNode *heap);
+
+#endif
+