add desktop notifications

Motivation: Hook scripts for nautilus or other file managers
need to provide the user with feedback that a file is being downloaded.

This commit was sponsored by THM Schoemaker.

Types/DesktopNotify.hs

@@ -0,0 +1,27 @@
+{- git-annex DesktopNotify type
+ -
+ - Copyright 2014 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Types.DesktopNotify where
+
+import Data.Monoid
+
+data DesktopNotify = DesktopNotify
+	{ notifyStart :: Bool
+	, notifyFinish :: Bool
+	}
+	deriving (Show)
+
+instance Monoid DesktopNotify where
+	mempty = DesktopNotify False False
+	mappend (DesktopNotify s1 f1) (DesktopNotify s2 f2) =
+		DesktopNotify (s1 || s2) (f1 || f2)
+
+mkNotifyStart :: DesktopNotify
+mkNotifyStart = DesktopNotify True False
+
+mkNotifyFinish :: DesktopNotify
+mkNotifyFinish = DesktopNotify False True