better fix for Issue #629 Recursive generic types not working

compiler/types.nim

@@ -825,8 +825,6 @@ proc SameTypeAux(x, y: PType, c: var TSameTypeClosure): bool =
     of dcEqOrDistinctOf:
       while a.kind == tyDistinct: a = a.sons[0]
       if a.kind != b.kind: return false  
-  if x.Kind == tyGenericInst or y.Kind == tyGenericInst: 
-    c.cmp = dcEqIgnoreDistinct    
   case a.Kind
   of tyEmpty, tyChar, tyBool, tyNil, tyPointer, tyString, tyCString,
      tyInt..tyBigNum, tyStmt:
@@ -839,8 +837,13 @@ proc SameTypeAux(x, y: PType, c: var TSameTypeClosure): bool =
       result = sameObjectStructures(a, b, c) and sameFlags(a, b)
   of tyDistinct:
     CycleCheck()
-    if c.cmp == dcEq: result = sameTypeAux(a, b, c) and sameFlags(a, b)
-    else: result = sameTypeAux(a.sons[0], b.sons[0], c) and sameFlags(a, b)
+    if c.cmp == dcEq:      
+      result = false      
+      if a.sym != nil and b.sym != nil:
+        if a.sym.name == b.sym.name:
+          result = sameTypeAux(a.sons[0], b.sons[0], c) and sameFlags(a, b)      
+    else:           
+      result = sameTypeAux(a.sons[0], b.sons[0], c) and sameFlags(a, b)
   of tyEnum, tyForward, tyProxy:
     # XXX generic enums do not make much sense, but require structural checking
     result = a.id == b.id and sameFlags(a, b)