add support for staging other types of blobs, like symlinks, into the index

Also added a utility TopFilePath type, which could stand to be used more
widely.

Git/FilePath.hs

@@ -0,0 +1,34 @@
+{- git FilePath library
+ -
+ - Different git commands use different types of FilePaths to refer to
+ - files in the repository. Some commands use paths relative to the
+ - top of the repository even when run in a subdirectory. Adding some
+ - types helps keep that straight.
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Git.FilePath (
+	TopFilePath,
+	getTopFilePath,
+	toTopFilePath,
+	asTopFilePath,
+) where
+
+import Common
+import Git
+
+{- A FilePath, relative to the top of the git repository. -}
+newtype TopFilePath = TopFilePath { getTopFilePath :: FilePath }
+
+{- The input FilePath can be absolute, or relative to the CWD. -}
+toTopFilePath :: FilePath -> Git.Repo -> IO TopFilePath
+toTopFilePath file repo = TopFilePath <$>
+	relPathDirToFile (repoPath repo) <$> absPath file
+
+{- The input FilePath must already be relative to the top of the git
+ - repository -}
+asTopFilePath :: FilePath -> TopFilePath
+asTopFilePath file = TopFilePath file