Add a test for better exceptions when ewxecuting programs

tests/all.T

@@ -32,3 +32,4 @@ test('T3994', only_ways(['threaded1','threaded2']), compile_and_run, [''])
 test('T4889', normal, compile_and_run, [''])
 
 test('process009', when(opsys('mingw32'), skip), compile_and_run, [''])
+test('process010', normal, compile_and_run, [''])

tests/process010.hs

+
+import System.IO.Error
+import System.Process
+
+main :: IO ()
+main = do run "/bin/true"
+          run "/bin/false"
+          run "/non/existent"
+          putStrLn "Done"
+
+run :: FilePath -> IO ()
+run fp = (rawSystem fp [] >>= print)
+         `catchIOError` \e -> putStrLn ("Exc: " ++ show e)

tests/process010.stdout

+ExitSuccess
+ExitFailure 1
+Exc: /non/existent: rawSystem: runInteractiveProcess: exec: does not exist (No such file or directory)
+Done