Update examples

testsuite/unload/sjwtrap/Makefile

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+TEST=   unload/sjwtrap
+EXTRA_OBJS=Null.o
+TOP=../../..
+include ../../build.mk

testsuite/unload/sjwtrap/Null.hs

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+module Null where
+
+import qualified Prelude
+import API
+
+resource = null

testsuite/unload/sjwtrap/api/API.hs

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+{-# OPTIONS -fglasgow-exts #-}
+
+module API where
+
+data Null = Null { a, b :: Int }
+
+null :: Null
+null = Null { a = 42 , b = 1 }
+

testsuite/unload/sjwtrap/prog/Main.hs

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+
+import System.Plugins
+import API
+
+--
+-- what happens if we try to use code that has been unloaded?
+--
+
+main = do 
+    m_v   <- load "../Null.o" ["../api"] [] "resource"
+    (m,v) <- case m_v of
+        LoadSuccess m v -> return (m,v)
+        _               -> error "load failed"
+    putStrLn ( show (a v) )
+    unload m

testsuite/unload/sjwtrap/prog/expected

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+42