fine-grained locking when annex.pidlock is enabled

This locking has been missing from the beginning of annex.pidlock.
It used to be possble, when two threads are doing conflicting things,
for both to run at the same time despite using locking. Seems likely
that nothing actually had a problem, but it was possible, and this
eliminates that possible source of failure.

Sponsored-by: Dartmouth College's Datalad project

Utility/LockPool/LockHandle.hs

@@ -8,7 +8,7 @@
 {-# LANGUAGE CPP #-}
 
 module Utility.LockPool.LockHandle (
-	LockHandle,
+	LockHandle(..),
 	FileLockOps(..),
 	dropLock,
 #ifndef mingw32_HOST_OS
@@ -86,4 +86,3 @@ mkLockHandle :: P.LockHandle -> FileLockOps -> IO LockHandle
 mkLockHandle ph fo = do
 	atomically $ P.registerCloseLockFile ph (fDropLock fo)
 	return $ LockHandle ph fo
-