bugfix: type alias to generic; generic type not stripped away from for loop variable

tests/compile/tgeneric.nim

@@ -0,0 +1,11 @@
+import tables
+
+type
+  TX = TTable[string, int]
+
+proc foo(models: seq[TTable[string, float]]): seq[float] =
+  result = @[]
+  for model in models.items:
+    result.add model["foobar"]
+
+