Testsuite: add test for #10781

testsuite/tests/rename/should_fail/T10781.hs

+module T10781 where
+{- ghc-7.10.2 reported:
+
+T10781.hs:6:5:
+    Found hole ‘_name’ with type: t
+    Where: ‘t’ is a rigid type variable bound by
+               the inferred type of f :: t at T10781.hs:6:1
+    Relevant bindings include f :: t (bound at T10781.hs:6:1)
+    In the expression: Foo._name
+    In an equation for ‘f’: f = Foo._name
+-}
+f = Foo._name

testsuite/tests/rename/should_fail/T10781.stderr

+
+T10781.hs:12:5: error: Not in scope: ‘Foo._name’

testsuite/tests/rename/should_fail/all.T

@@ -137,3 +137,4 @@ test('T9032',
 test('T10618', normal, compile_fail, [''])
 test('T10668', normal, compile_fail, [''])
 test('T5001b', normal, compile_fail, [''])
+test('T10781', normal, compile_fail, [''])