Switch to using relative paths to the git repository.

This allows the git repository to be moved while git-annex is running in
it, with fewer problems.

On Windows, this avoids some of the problems with the absurdly small
MAX_PATH of 260 bytes. In particular, git-annex repositories should
work in deeper/longer directory structures than before. See
http://git-annex.branchable.com/bugs/__34__git-annex:_direct:_1_failed__34___on_Windows/

There are several possible ways this change could break git-annex:

1. If it changes its working directory while it's running, that would
   be Bad News. Good news everyone! git-annex never does so. It would also
   break thread safety, so all such things were stomped out long ago.

2. parentDir "." -> "" which is not a valid path. I had to fix one
   instace of this, and I should probably wipe all calls to parentDir out
   of the git-annex code base; it was never a good idea.

3. Things like relPathDirToFile require absolute input paths,
   and code assumes that the git repo path is absolute and passes it to it
   as-is. In the case of relPathDirToFile, I converted it to not make
   this assumption.

Currently, the test suite has 16 failures.

1 files changed, 14 insertions, 9 deletions

diff --git a/Utility/Path.hs b/Utility/Path.hs
index c3e893d16..7427bfe27 100644
--- a/Utility/Path.hs
+++ b/Utility/Path.hs
@@ -126,14 +126,19 @@ absPath file = do
  -    relPathCwdToFile "/tmp/foo/bar" == "" 
  -}
 relPathCwdToFile :: FilePath -> IO FilePath
-relPathCwdToFile f = relPathDirToFile <$> getCurrentDirectory <*> absPath f
+relPathCwdToFile f = do
+	c <- getCurrentDirectory
+	relPathDirToFile c f
 
-{- Constructs a relative path from a directory to a file.
- -
- - Both must be absolute, and cannot contain .. etc. (eg use absPath first).
+{- Constructs a relative path from a directory to a file. -}
+relPathDirToFile :: FilePath -> FilePath -> IO FilePath
+relPathDirToFile from to = relPathDirToFileAbs <$> absPath from <*> absPath to
+
+{- This requires the first path to be absolute, and the
+ - second path cannot contain ../ or ./
  -}
-relPathDirToFile :: FilePath -> FilePath -> FilePath
-relPathDirToFile from to = join s $ dotdots ++ uncommon
+relPathDirToFileAbs :: FilePath -> FilePath -> FilePath
+relPathDirToFileAbs from to = join s $ dotdots ++ uncommon
   where
 	s = [pathSeparator]
 	pfrom = split s from
@@ -149,7 +154,7 @@ prop_relPathDirToFile_basics from to
 	| from == to = null r
 	| otherwise = not (null r)
   where
-	r = relPathDirToFile from to 
+	r = relPathDirToFileAbs from to 
 
 prop_relPathDirToFile_regressionTest :: Bool
 prop_relPathDirToFile_regressionTest = same_dir_shortcurcuits_at_difference
@@ -158,7 +163,7 @@ prop_relPathDirToFile_regressionTest = same_dir_shortcurcuits_at_difference
 	 - location, but it's not really the same directory.
 	 - Code used to get this wrong. -}
 	same_dir_shortcurcuits_at_difference =
-		relPathDirToFile (joinPath [pathSeparator : "tmp", "r", "lll", "xxx", "yyy", "18"])
+		relPathDirToFileAbs (joinPath [pathSeparator : "tmp", "r", "lll", "xxx", "yyy", "18"])
 			(joinPath [pathSeparator : "tmp", "r", ".git", "annex", "objects", "18", "gk", "SHA256-foo", "SHA256-foo"])
 				== joinPath ["..", "..", "..", "..", ".git", "annex", "objects", "18", "gk", "SHA256-foo", "SHA256-foo"]
 
@@ -187,7 +192,7 @@ relHome :: FilePath -> IO String
 relHome path = do
 	home <- myHomeDir
 	return $ if dirContains home path
-		then "~/" ++ relPathDirToFile home path
+		then "~/" ++ relPathDirToFileAbs home path
 		else path
 
 {- Checks if a command is available in PATH.