Move rbtree.c from src/backend/utils/misc to src/backend/lib.

We have other general-purpose data structures in src/backend/lib, so it
seems like a better home for the red-black tree as well.

src/include/lib/rbtree.h

@@ -0,0 +1,66 @@
+/*-------------------------------------------------------------------------
+ *
+ * rbtree.h
+ *	  interface for PostgreSQL generic Red-Black binary tree package
+ *
+ * Copyright (c) 2009-2014, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *		src/include/lib/rbtree.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef RBTREE_H
+#define RBTREE_H
+
+/*
+ * RBNode is intended to be used as the first field of a larger struct,
+ * whose additional fields carry whatever payload data the caller needs
+ * for a tree entry.  (The total size of that larger struct is passed to
+ * rb_create.)	RBNode is declared here to support this usage, but
+ * callers must treat it as an opaque struct.
+ */
+typedef struct RBNode
+{
+	char		iteratorState;	/* workspace for iterating through tree */
+	char color;					/* node's current color, red or black */
+	struct RBNode *left;		/* left child, or RBNIL if none */
+	struct RBNode *right;		/* right child, or RBNIL if none */
+	struct RBNode *parent;		/* parent, or NULL (not RBNIL!) if none */
+} RBNode;
+
+/* Opaque struct representing a whole tree */
+typedef struct RBTree RBTree;
+
+/* Available tree iteration orderings */
+typedef enum RBOrderControl
+{
+	LeftRightWalk,				/* inorder: left child, node, right child */
+	RightLeftWalk,				/* reverse inorder: right, node, left */
+	DirectWalk,					/* preorder: node, left child, right child */
+	InvertedWalk				/* postorder: left child, right child, node */
+} RBOrderControl;
+
+/* Support functions to be provided by caller */
+typedef int (*rb_comparator) (const RBNode *a, const RBNode *b, void *arg);
+typedef void (*rb_combiner) (RBNode *existing, const RBNode *newdata, void *arg);
+typedef RBNode *(*rb_allocfunc) (void *arg);
+typedef void (*rb_freefunc) (RBNode *x, void *arg);
+
+extern RBTree *rb_create(Size node_size,
+		  rb_comparator comparator,
+		  rb_combiner combiner,
+		  rb_allocfunc allocfunc,
+		  rb_freefunc freefunc,
+		  void *arg);
+
+extern RBNode *rb_find(RBTree *rb, const RBNode *data);
+extern RBNode *rb_leftmost(RBTree *rb);
+
+extern RBNode *rb_insert(RBTree *rb, const RBNode *data, bool *isNew);
+extern void rb_delete(RBTree *rb, RBNode *node);
+
+extern void rb_begin_iterate(RBTree *rb, RBOrderControl ctrl);
+extern RBNode *rb_iterate(RBTree *rb);
+
+#endif   /* RBTREE_H */