Fix generics inheritance issues

tests/generics/t88.nim

@@ -0,0 +1,25 @@
+# Issue 88
+
+type
+  BaseClass[V] = object of RootObj
+    b: V
+
+proc new[V](t: typedesc[BaseClass], v: V): BaseClass[V] =
+  BaseClass[V](b: v)
+
+proc baseMethod[V](v: BaseClass[V]): V = v.b
+proc overridedMethod[V](v: BaseClass[V]): V = v.baseMethod
+
+type
+  ChildClass[V] = object of BaseClass[V]
+    c: V
+
+proc new[V](t: typedesc[ChildClass], v1, v2: V): ChildClass[V] =
+  ChildClass[V](b: v1, c: v2)
+
+proc overridedMethod[V](v: ChildClass[V]): V = v.c
+
+let c = ChildClass[string].new("Base", "Child")
+
+assert c.baseMethod == "Base"
+assert c.overridedMethod == "Child"