Import 'rtree' extension. (CVS 5159)

FossilOrigin-Name: b104dcd6adadbd3fe15a348fe9d4d290119e139e
diff --git a/main.mk b/main.mk
index 6505f38..c841b29 100644
--- a/main.mk
+++ b/main.mk
@@ -58,7 +58,7 @@
          select.o table.o $(TCLOBJ) tokenize.o trigger.o \
          update.o util.o vacuum.o \
          vdbe.o vdbeapi.o vdbeaux.o vdbeblob.o vdbefifo.o vdbemem.o \
-         where.o utf.o legacy.o vtab.o
+         where.o utf.o legacy.o vtab.o rtree.o
 
 EXTOBJ = icu.o
 EXTOBJ += fts1.o \
@@ -412,6 +412,9 @@
 fts3_tokenizer1.o:	$(TOP)/ext/fts3/fts3_tokenizer1.c $(HDR) $(EXTHDR)
 	$(TCCX) -DSQLITE_CORE -c $(TOP)/ext/fts3/fts3_tokenizer1.c
 
+rtree.o:	$(TOP)/ext/rtree/rtree.c $(HDR) $(EXTHDR)
+	$(TCCX) -DSQLITE_CORE -c $(TOP)/ext/rtree/rtree.c
+
 
 # Rules for building test programs and for running tests
 #