rename key2file and file2key

What these generate is not really suitable to be used as a filename,
which is why keyFile and fileKey further escape it. These are just
serializing Keys.

Also removed a quickcheck test that was very unlikely to test anything
useful, since it relied on random chance creating something that looks
like a serialized key. The other test is sufficient for testing what
that was intended to test anyway.

Logs/Smudge.hs

@@ -16,7 +16,7 @@ smudgeLog :: Key -> TopFilePath -> Annex ()
 smudgeLog k f = do
 	logf <- fromRepo gitAnnexSmudgeLog
 	appendLogFile logf gitAnnexSmudgeLock $ 
-		key2file k ++ " " ++ getTopFilePath f
+		serializeKey k ++ " " ++ getTopFilePath f
 
 -- | Streams all smudged files, and then empties the log at the end.
 --
@@ -36,5 +36,5 @@ streamSmudged a = do
 	parse l = 
 		let (ks, f) = separate (== ' ') l
 		in do
-			k <- file2key ks
+			k <- deserializeKey ks
 			return (k, asTopFilePath f)