type constraints; tuple lifting

tests/reject/tconstraints.nim

@@ -0,0 +1,18 @@
+discard """
+  line: 15
+  errormsg: "type mismatch: got (int)"
+"""
+
+proc myGenericProc[T: object|tuple|ptr|ref|distinct](x: T): string = 
+  result = $x
+
+type
+  TMyObj = tuple[x, y: int]
+
+var
+  x: TMyObj
+
+assert myGenericProc(232) == "232"
+assert myGenericProc(x) == "(x: 0, y: 0)"
+
+