use lock pools throughout git-annex

The one exception is in Utility.Daemon. As long as a process only
daemonizes once, which seems reasonable, and as long as it avoids calling
checkDaemon once it's already running as a daemon, the fcntl locking
gotchas won't be a problem there.

Annex.LockFile has it's own separate lock pool layer, which has been
renamed to LockCache. This is a persistent cache of locks that persist
until closed.

This is not quite done; lockContent stil needs to be converted.

Types/LockCache.hs

@@ -0,0 +1,16 @@
+{- git-annex lock cache data types
+ - 
+ - Copyright 2014 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Types.LockCache (
+	LockCache,
+	LockHandle
+) where
+
+import qualified Data.Map as M
+import Utility.LockPool
+
+type LockCache = M.Map FilePath LockHandle