added gcleak4.nim test; fails in debug mode

tests/gc/gcleak4.nim

@@ -0,0 +1,42 @@
+discard """
+  outputsub: "no leak: "
+"""
+
+when defined(GC_setMaxPause):
+  GC_setMaxPause 2_000
+
+type
+  TExpr = object ## abstract base class for an expression
+  PLiteral = ref TLiteral
+  TLiteral = object of TExpr
+    x: int
+  TPlusExpr = object of TExpr
+    a, b: ref TExpr
+    
+method eval(e: ref TExpr): int =
+  # override this base method
+  quit "to override!"
+
+method eval(e: ref TLiteral): int = return e.x
+
+method eval(e: ref TPlusExpr): int =
+  # watch out: relies on dynamic binding
+  return eval(e.a) + eval(e.b)
+
+proc newLit(x: int): ref TLiteral =
+  new(result)
+  {.watchpoint: result.}
+  result.x = x
+  
+proc newPlus(a, b: ref TExpr): ref TPlusExpr =
+  new(result)
+  {.watchpoint: result.}
+  result.a = a
+  result.b = b
+
+for i in 0..100_000:
+  if eval(newPlus(newPlus(newLit(1), newLit(2)), newLit(4))) != 7:
+    quit "error: wrong result"
+  if getOccupiedMem() > 3000_000: quit("still a leak!")
+
+echo "no leak: ", getOccupiedMem()