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.hs

@@ -124,7 +124,7 @@ urlLogFile config key = branchHashDir config key </> keyFile key ++ urlLogExt
 {- Old versions stored the urls elsewhere. -}
 oldurlLogs :: GitConfig -> Key -> [FilePath]
 oldurlLogs config key =
-	[ "remote/web" </> hdir </> key2file key ++ ".log"
+	[ "remote/web" </> hdir </> serializeKey key ++ ".log"
 	, "remote/web" </> hdir </> keyFile key ++ ".log"
 	]
   where