Clean up handling of git directory and git worktree.

Baked into the code was an assumption that a repository's git directory
could be determined by adding ".git" to its work tree (or nothing for bare
repos). That fails when core.worktree, or GIT_DIR and GIT_WORK_TREE are
used to separate the two.

This was attacked at the type level, by storing the gitdir and worktree
separately, so Nothing for the worktree means a bare repo.

A complication arose because we don't learn where a repository is bare
until its configuration is read. So another Location type handles
repositories that have not had their config read yet. I am not entirely
happy with this being a Location type, rather than representing them
entirely separate from the Git type. The new code is not worse than the
old, but better types could enforce more safety.

Added support for core.worktree. Overriding it with -c isn't supported
because it's not really clear what to do if a git repo's config is read, is
not bare, and is then overridden to bare. What is the right git directory
in this case? I will worry about this if/when someone has a use case for
overriding core.worktree with -c. (See Git.Config.updateLocation)

Also removed and renamed some functions like gitDir and workTree that
misused git's terminology.

One minor regression is known: git annex add in a bare repository does not
print a nice error message, but runs git ls-files in a way that fails
earlier with a less nice error message. This is because before --work-tree
was always passed to git commands, even in a bare repo, while now it's not.

2 files changed, 4 insertions, 3 deletions

diff --git a/Annex/Content.hs b/Annex/Content.hs
index 2142d1f09..26b332e24 100644
--- a/Annex/Content.hs
+++ b/Annex/Content.hs
@@ -34,6 +34,7 @@ import Common.Annex
 import Logs.Location
 import Annex.UUID
 import qualified Git
+import qualified Git.Config
 import qualified Annex
 import qualified Annex.Queue
 import qualified Annex.Branch
@@ -303,7 +304,7 @@ saveState oneshot = doSideAction $ do
 		ifM alwayscommit
 			( Annex.Branch.commit "update" , Annex.Branch.stage)
 	where
-		alwayscommit = fromMaybe True . Git.configTrue
+		alwayscommit = fromMaybe True . Git.Config.isTrue
 			<$> getConfig (annexConfig "alwayscommit") ""
 
 {- Downloads content from any of a list of urls. -}
diff --git a/Annex/Ssh.hs b/Annex/Ssh.hs
index f0824b119..8bd4fe33a 100644
--- a/Annex/Ssh.hs
+++ b/Annex/Ssh.hs
@@ -14,7 +14,7 @@ import qualified Data.Map as M
 
 import Common.Annex
 import Annex.LockPool
-import qualified Git
+import qualified Git.Config
 import Config
 import qualified Build.SysConfig as SysConfig
 import Annex.Perms
@@ -47,7 +47,7 @@ sshInfo (host, port) = ifM caching
 	)
 	where
 		caching = fromMaybe SysConfig.sshconnectioncaching 
-			. Git.configTrue
+			. Git.Config.isTrue
 			<$> getConfig (annexConfig "sshcaching") ""
 
 cacheParams :: FilePath -> [CommandParam]