shared repository content file permissions for v9

v9 will not need to write to annex content files in order to lock them,
so freezeContent removes the write bit in a shared repository, the same
as in any other repository.

checkContentWritePerm makes sure that the write perm is not set, which
will let git-annex fsck fix up the permissions. Upgrading to v9
will need to fix the permissions as well, but it seems likely there will
be situations where the user git-annex is running an upgrade as cannot,
so it will have to leave the write bit set. In such a case, git-annex
fsck can fix it later.

Sponsored-by: Dartmouth College's Datalad project

Annex/Version.hs

@@ -1,6 +1,6 @@
 {- git-annex repository versioning
  -
- - Copyright 2010-2021 Joey Hess <id@joeyh.name>
+ - Copyright 2010-2022 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -54,3 +54,8 @@ setVersion (RepoVersion v) = setConfig versionField (show v)
 
 removeVersion :: Annex ()
 removeVersion = unsetConfig versionField
+
+versionNeedsWritableContentFiles :: Maybe RepoVersion -> Bool
+versionNeedsWritableContentFiles (Just v) 
+	| v >= RepoVersion 9 = False
+versionNeedsWritableContentFiles _ = True