support commit.gpgsign

Support users who have set commit.gpgsign, by disabling gpg signatures for
git-annex branch commits and commits made by the assistant.

The thinking here is that a user sets commit.gpgsign intending the commits
that they manually initiate to be gpg signed. But not commits made in the
background, whether by a deamon or implicitly to the git-annex branch.
gpg signing those would be at best a waste of CPU and at worst would fail,
or flood the user with gpg passphrase prompts, or put their signature on
changes they did not directly do.

See Debian bug #753720.

Also makes all commits done by git-annex go through a few central control
points, to make such changes easier in future.

Also disables commit.gpgsign in the test suite.

This commit was sponsored by Antoine Boegli.

Annex/Direct.hs

@@ -151,8 +151,8 @@ addDirect file cache = do
  - Then the work tree is updated to reflect the merge, and
  - finally, the merge is committed and the real index updated.
  -}
-mergeDirect :: Maybe Git.Ref -> Maybe Git.Ref -> Git.Branch -> Annex Bool -> Annex Bool
-mergeDirect startbranch oldref branch resolvemerge = do
+mergeDirect :: Maybe Git.Ref -> Maybe Git.Ref -> Git.Branch -> Annex Bool -> Git.Branch.CommitMode -> Annex Bool
+mergeDirect startbranch oldref branch resolvemerge commitmode = do
 	-- Use the index lock file as the temp index file.
 	-- This is actually what git does when updating the index,
 	-- and so it will prevent other git processes from making
@@ -168,19 +168,19 @@ mergeDirect startbranch oldref branch resolvemerge = do
 		createDirectoryIfMissing True d
 
 	withIndexFile tmpi $ do
-		merged <- stageMerge d branch
+		merged <- stageMerge d branch commitmode
 		r <- if merged
 			then return True
 			else resolvemerge
 		mergeDirectCleanup d (fromMaybe Git.Sha.emptyTree oldref)
-		mergeDirectCommit merged startbranch branch
+		mergeDirectCommit merged startbranch branch commitmode
 		liftIO $ rename tmpi reali
 		return r
 
 {- Stage a merge into the index, avoiding changing HEAD or the current
  - branch. -}
-stageMerge :: FilePath -> Git.Branch -> Annex Bool
-stageMerge d branch = do
+stageMerge :: FilePath -> Git.Branch -> Git.Branch.CommitMode -> Annex Bool
+stageMerge d branch commitmode = do
 	-- XXX A bug in git makes stageMerge unsafe to use if the git repo
 	-- is configured with core.symlinks=false
 	-- Using mergeNonInteractive is not ideal though, since it will
@@ -190,7 +190,7 @@ stageMerge d branch = do
 	-- <http://marc.info/?l=git&m=140262402204212&w=2>
 	merger <- ifM (coreSymlinks <$> Annex.getGitConfig)
 		( return Git.Merge.stageMerge
-		, return Git.Merge.mergeNonInteractive
+		, return $ \ref -> Git.Merge.mergeNonInteractive ref commitmode
 		) 
 	inRepo $ \g -> merger branch $ 
 		g { location = Local { gitdir = Git.localGitDir g, worktree = Just d } }
@@ -198,8 +198,8 @@ stageMerge d branch = do
 {- Commits after a direct mode merge is complete, and after the work
  - tree has been updated by mergeDirectCleanup.
  -}
-mergeDirectCommit :: Bool -> Maybe Git.Ref -> Git.Branch -> Annex ()
-mergeDirectCommit allowff old branch = do
+mergeDirectCommit :: Bool -> Maybe Git.Ref -> Git.Branch -> Git.Branch.CommitMode -> Annex ()
+mergeDirectCommit allowff old branch commitmode = do
 	void preCommitDirect
 	d <- fromRepo Git.localGitDir
 	let merge_head = d </> "MERGE_HEAD"
@@ -211,7 +211,7 @@ mergeDirectCommit allowff old branch = do
 			msg <- liftIO $
 				catchDefaultIO ("merge " ++ fromRef branch) $
 					readFile merge_msg
-			void $ inRepo $ Git.Branch.commit False msg
+			void $ inRepo $ Git.Branch.commit commitmode False msg
 				Git.Ref.headRef [Git.Ref.headRef, branch]
 		)
 	liftIO $ mapM_ nukeFile [merge_head, merge_msg, merge_mode]