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.

Git/Branch.hs

@@ -103,6 +103,28 @@ fastForward branch (first:rest) repo =
 			(False, True) -> findbest c rs -- worse
 			(False, False) -> findbest c rs -- same
 
+{- The user may have set commit.gpgsign, indending all their manual
+ - commits to be signed. But signing automatic/background commits could
+ - easily lead to unwanted gpg prompts or failures.
+ -}
+data CommitMode = ManualCommit | AutomaticCommit
+	deriving (Eq)
+
+{- Commit via the usual git command. -}
+commitCommand :: CommitMode -> [CommandParam] -> Repo -> IO Bool
+commitCommand = commitCommand' runBool
+
+{- Commit will fail when the tree is clean. This suppresses that error. -}
+commitQuiet :: CommitMode -> [CommandParam] -> Repo -> IO ()
+commitQuiet commitmode ps = void . tryIO . commitCommand' runQuiet commitmode ps
+
+commitCommand' :: ([CommandParam] -> Repo -> IO a) -> CommitMode -> [CommandParam] -> Repo -> IO a
+commitCommand' runner commitmode ps = runner (Param "commit" : ps')
+  where
+	ps'
+		| commitmode == AutomaticCommit = Param "--no-gpg-sign" : ps
+		| otherwise = ps
+
 {- Commits the index into the specified branch (or other ref), 
  - with the specified parent refs, and returns the committed sha.
  -
@@ -112,8 +134,8 @@ fastForward branch (first:rest) repo =
  - Unlike git-commit, does not run any hooks, or examine the work tree
  - in any way.
  -}
-commit :: Bool -> String -> Branch -> [Ref] -> Repo -> IO (Maybe Sha)
-commit allowempty message branch parentrefs repo = do
+commit :: CommitMode -> Bool -> String -> Branch -> [Ref] -> Repo -> IO (Maybe Sha)
+commit commitmode allowempty message branch parentrefs repo = do
 	tree <- getSha "write-tree" $
 		pipeReadStrict [Param "write-tree"] repo
 	ifM (cancommit tree)
@@ -126,16 +148,18 @@ commit allowempty message branch parentrefs repo = do
 		, return Nothing
 		)
   where
-	ps = concatMap (\r -> ["-p", fromRef r]) parentrefs
+	ps = 
+		(if commitmode == AutomaticCommit then ["--no-gpg-sign"] else [])
+		++ concatMap (\r -> ["-p", fromRef r]) parentrefs
 	cancommit tree
 		| allowempty = return True
 		| otherwise = case parentrefs of
 			[p] -> maybe False (tree /=) <$> Git.Ref.tree p repo
 			_ -> return True
 
-commitAlways :: String -> Branch -> [Ref] -> Repo -> IO Sha
-commitAlways message branch parentrefs repo = fromJust
-	<$> commit True message branch parentrefs repo
+commitAlways :: CommitMode -> String -> Branch -> [Ref] -> Repo -> IO Sha
+commitAlways commitmode message branch parentrefs repo = fromJust
+	<$> commit commitmode True message branch parentrefs repo
 
 {- A leading + makes git-push force pushing a branch. -}
 forcePush :: String -> String