add annex.dbdir (WIP)

WIP: This is mostly complete, but there is a problem: createDirectoryUnder
throws an error when annex.dbdir is set to outside the git repo.

annex.dbdir is a workaround for filesystems where sqlite does not work,
due to eg, the filesystem not properly supporting locking.

It's intended to be set before initializing the repository. Changing it
in an existing repository can be done, but would be the same as making a
new repository and moving all the annexed objects into it. While the
databases get recreated from the git-annex branch in that situation, any
information that is in the databases but not stored in the branch gets
lost. It may be that no information ever gets stored in the databases
that cannot be reconstructed from the branch, but I have not verified
that.

Sponsored-by: Dartmouth College's Datalad project

Upgrade/V7.hs

@@ -37,17 +37,17 @@ upgrade automatic = do
 	-- The old content identifier database is deleted here, but the
 	-- new database is not populated. It will be automatically
 	-- populated from the git-annex branch the next time it is used.
-	removeOldDb gitAnnexContentIdentifierDbDirOld
+	removeOldDb . fromRawFilePath =<< fromRepo gitAnnexContentIdentifierDbDirOld
 	liftIO . removeWhenExistsWith R.removeLink
 		=<< fromRepo gitAnnexContentIdentifierLockOld
 
 	-- The export databases are deleted here. The new databases
 	-- will be populated by the next thing that needs them, the same
 	-- way as they would be in a fresh clone.
-	removeOldDb gitAnnexExportDir
+	removeOldDb . fromRawFilePath =<< calcRepo' gitAnnexExportDir
 
 	populateKeysDb
-	removeOldDb gitAnnexKeysDbOld
+	removeOldDb . fromRawFilePath =<< fromRepo gitAnnexKeysDbOld
 	liftIO . removeWhenExistsWith R.removeLink
 		=<< fromRepo gitAnnexKeysDbIndexCacheOld
 	liftIO . removeWhenExistsWith R.removeLink
@@ -72,9 +72,8 @@ gitAnnexContentIdentifierDbDirOld r = gitAnnexDir r P.</> "cids"
 gitAnnexContentIdentifierLockOld :: Git.Repo -> RawFilePath
 gitAnnexContentIdentifierLockOld r = gitAnnexContentIdentifierDbDirOld r <> ".lck"
 
-removeOldDb :: (Git.Repo -> RawFilePath) -> Annex ()
-removeOldDb getdb = do
-	db <- fromRawFilePath <$> fromRepo getdb
+removeOldDb :: FilePath -> Annex ()
+removeOldDb db =
 	whenM (liftIO $ doesDirectoryExist db) $ do
 		v <- liftIO $ tryNonAsync $
 #if MIN_VERSION_directory(1,2,7)

Upgrade/V9.hs

@@ -71,7 +71,8 @@ performUpgrade automatic = do
 	
 	{- Take a lock to ensure that there are no other git-annex
 	 - processes running that are using the old content locking method. -}
-	withExclusiveLock gitAnnexContentLockLock $ do
+	lck <- fromRepo gitAnnexContentLockLock
+	withExclusiveLock lck $ do
 		{- When core.sharedRepository is set, object files
 		 - used to have their write bits set. That can now be
 		 - removed, if the user the upgrade is running as has