Branch handling improvements

Support creating the branch.

Unified branch state into a single data type.

Only commit changes when the index has been changed.

Types/BranchState.hs

@@ -0,0 +1,18 @@
+{- git-annex BranchState data type
+ -
+ - Copyright 2011 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Types.BranchState where
+
+data BranchState = BranchState {
+	branchUpdated :: Bool,
+	branchChanged :: Bool,
+	cachedFile :: Maybe FilePath,
+	cachedContent :: String
+}
+
+startBranchState :: BranchState
+startBranchState = BranchState False False Nothing ""