TypeFamilies: should_compile/Simple22

* Demonstrates a bug in TcUnify.tcSubFun found by Andrew Appleyard

testsuite/tests/ghc-regress/indexed-types/should_compile/Simple22.hs

+{-# LANGUAGE TypeFamilies #-}
+
+module ShouldCompile where
+
+data X1 = X1
+
+class C t where
+    type D t
+    f :: t -> D t -> ()
+
+instance C X1 where
+    type D X1 = Bool -> Bool
+    f _ h = ()
+
+foo = f X1 (\x -> x)

testsuite/tests/ghc-regress/indexed-types/should_compile/all.T

@@ -21,6 +21,7 @@ test('Simple17', expect_fail, compile, [''])
 test('Simple18', normal, compile, [''])
 test('Simple19', normal, compile, [''])
 test('Simple20', normal, compile, [''])
+test('Simple22', normal, compile, [''])
 
 test('ind1', normal, compile, [''])
 test('ind2', expect_fail_ways_if_compiler_lt('ghc','6.9',['profc','profasm']),