add git annex view command

(And a vpop command, which is still a bit buggy.)

Still need to do vadd and vrm, though this also adds their documentation.

Currently not very happy with the view log data serialization. I had to
lose the TDFA regexps temporarily, so I can have Read/Show instances of
View. I expect the view log format will change in some incompatable way
later, probably adding last known refs for the parent branch to View
or something like that.

Anyway, it basically works, although it's a bit slow looking up the
metadata. The actual git branch construction is about as fast as it can be
using the current git plumbing.

This commit was sponsored by Peter Hogg.

Annex/Branch.hs

@@ -5,8 +5,6 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
-{-# LANGUAGE CPP #-}
-
 module Annex.Branch (
 	fullname,
 	name,
@@ -30,11 +28,11 @@ module Annex.Branch (
 import qualified Data.ByteString.Lazy.Char8 as L
 import qualified Data.Set as S
 import qualified Data.Map as M
-import qualified Control.Exception as E
 
 import Common.Annex
 import Annex.BranchState
 import Annex.Journal
+import Annex.Index
 import qualified Git
 import qualified Git.Command
 import qualified Git.Ref
@@ -47,15 +45,12 @@ import Git.Types
 import Git.FilePath
 import Annex.CatFile
 import Annex.Perms
-import qualified Annex
-import Utility.Env
 import Logs
 import Logs.Transitions
 import Logs.Trust.Pure
 import Annex.ReplaceFile
 import qualified Annex.Queue
 import Annex.Branch.Transitions
-import Annex.Exception
 
 {- Name of the branch that is used to store git-annex's information. -}
 name :: Git.Ref
@@ -338,32 +333,12 @@ withIndex = withIndex' False
 withIndex' :: Bool -> Annex a -> Annex a
 withIndex' bootstrapping a = do
 	f <- fromRepo gitAnnexIndex
-	g <- gitRepo
-#ifdef __ANDROID__
-	{- This should not be necessary on Android, but there is some
-	 - weird getEnvironment breakage. See
-	 - https://github.com/neurocyte/ghc-android/issues/7
-	 - Use getEnv to get some key environment variables that
-	 - git expects to have. -}
-	let keyenv = words "USER PATH GIT_EXEC_PATH HOSTNAME HOME"
-	let getEnvPair k = maybe Nothing (\v -> Just (k, v)) <$> getEnv k
-	e <- liftIO $ catMaybes <$> forM keyenv getEnvPair
-	let e' = ("GIT_INDEX_FILE", f):e
-#else
-	e <- liftIO getEnvironment
-	let e' = addEntry "GIT_INDEX_FILE" f e
-#endif
-	let g' = g { gitEnv = Just e' }
-
-	r <- tryAnnex $ do
-		Annex.changeState $ \s -> s { Annex.repo = g' }
+	withIndexFile f $ do
 		checkIndexOnce $ unlessM (liftIO $ doesFileExist f) $ do
 			unless bootstrapping create
 			createAnnexDirectory $ takeDirectory f
 			unless bootstrapping $ inRepo genIndex
 		a
-	Annex.changeState $ \s -> s { Annex.repo = (Annex.repo s) { gitEnv = gitEnv g} }
-	either E.throw return r
 
 {- Updates the branch's index to reflect the current contents of the branch.
  - Any changes staged in the index will be preserved.