add tail-call test

t/tail-call.scm

@@ -0,0 +1,13 @@
+(import (scheme base))
+
+;;; always returns zero
+(define (zero n)
+  (if (zero? n)
+      0
+      (zero (- n 1))))
+
+;;; using apply
+(define (zero-2 n)
+  (if (zero? n)
+      0
+      (apply zero-2 (list (- n 1)))))