avoid failure when gpgconf is not in path

Utility/Gpg.hs

@@ -439,8 +439,8 @@ testHarness tmpdir cmd a = ifM (inPath (unGpgCmd cmd))
 	-- other daemons. Stop them when done. This only affects
 	-- daemons started for the GNUPGHOME that was used.
 	-- Older gpg may not support this, so ignore failure.
-	stopgpgagent = void $ boolSystem "gpgconf"
-		[Param "--kill", Param "all"]
+	stopgpgagent = whenM (inPath "gpgconf") $
+		void $ boolSystem "gpgconf" [Param "--kill", Param "all"]
 
 	go (Just _) = Just <$> a
 	go Nothing = return Nothing

Utility/SafeCommand.hs

@@ -61,6 +61,8 @@ toCommand' (File s) = s
 
 -- | Run a system command, and returns True or False if it succeeded or failed.
 --
+-- (Throws an exception if the command is not found.)
+--
 -- This and other command running functions in this module log the commands
 -- run at debug level, using System.Log.Logger.
 boolSystem :: FilePath -> [CommandParam] -> IO Bool