enable LambdaCase and convert around 10% of places that could use it

Needs ghc 7.6.1, so minimum base version increased slightly. All builds
are well above this version of ghc, and debian oldstable is as well.

Code that could use lambdacase can be found by running:
git grep -B 1 'case ' | less
and searching in less for "<-"

This commit was sponsored by andrea rota.

1 files changed, 1 insertions, 1 deletions

diff --git a/Annex/Perms.hs b/Annex/Perms.hs
index 1ce342911..cfd25a5ee 100644
--- a/Annex/Perms.hs
+++ b/Annex/Perms.hs
@@ -112,7 +112,7 @@ isContentWritePermOk file = ifM crippledFileSystem
 	go AllShared = want writeModes
 	go _ = return True
 	want wantmode = do
-		mmode <- liftIO $ catchMaybeIO $ fileMode <$> getFileStatus file
+		liftIO $ catchMaybeIO $ fileMode <$> getFileStatus file
 		return $ case mmode of
 			Nothing -> True
 			Just havemode -> havemode == combineModes (havemode:wantmode)