annex.thin

Decided it's too scary to make v6 unlocked files have 1 copy by default,
but that should be available to those who need it. This is consistent with
git-annex not dropping unused content without --force, etc.

* Added annex.thin setting, which makes unlocked files in v6 repositories
  be hard linked to their content, instead of a copy. This saves disk
  space but means any modification of an unlocked file will lose the local
  (and possibly only) copy of the old version.
* Enable annex.thin by default on upgrade from direct mode to v6, since
  direct mode made the same tradeoff.
* fix: Adjusts unlocked files as configured by annex.thin.

Command/PreCommit.hs

@@ -52,7 +52,7 @@ seek ps = lockPreCommitHook $ ifM isDirect
 			, do
 				-- fix symlinks to files being committed
 				flip withFilesToBeCommitted ps $ \f -> 
-					maybe stop (Command.Fix.start f)
+					maybe stop (Command.Fix.start Command.Fix.FixSymlinks f)
 						=<< isAnnexLink f
 				-- inject unlocked files into the annex
 				-- (not needed when repo version uses