Fix a double free bug in PT_Free(), verify by calling vcl.discard.

src/patricia.c

@@ -323,8 +323,6 @@ PT_Free(struct pt_y *y)
 	CHECK_OBJ(y, PT_Y_MAGIC);
 	PT_Free(y->leaf[0]);
 	PT_Free(y->leaf[1]);
-	free(y->leaf[0]);
-	free(y->leaf[1]);
 	FREE_OBJ(y);
 }
 

src/tests/match.vtc

@@ -854,3 +854,9 @@ client c1 {
 } -run
 
 logexpect l1 -wait
+
+# Call vcl.discard to exercise set object finalization.
+varnish v1 -cliok "vcl.discard vcl1"
+varnish v1 -cliok "vcl.discard vcl2"
+
+varnish v1 -cli "vcl.list"

src/tests/prefix.vtc

@@ -1526,3 +1526,12 @@ client c1 {
 } -run
 
 logexpect l1 -wait
+
+
+# Call vcl.discard to exercise set object finalization.
+varnish v1 -cliok "vcl.discard vcl1"
+varnish v1 -cliok "vcl.discard vcl2"
+varnish v1 -cliok "vcl.discard vcl3"
+varnish v1 -cliok "vcl.discard vcl4"
+
+varnish v1 -cli "vcl.list"