remove Eq instance for InodeCache

There are two types of equality here, and which one is right varies,
so this forces me to consider and choose between them.

Based on this, I learned that the commit in git anex sync was
always doing a strong comparison, even when in a repository where
the inodes had changed. Fixed that.

Utility/InodeCache.hs

@@ -12,7 +12,11 @@ import System.Posix.Types
 import Utility.QuickCheck
 
 data InodeCache = InodeCache FileID FileOffset EpochTime
-	deriving (Eq, Show)
+	deriving (Show)
+
+compareStrong :: InodeCache -> InodeCache -> Bool
+compareStrong (InodeCache inode1 size1 mtime1) (InodeCache inode2 size2 mtime2) =
+	inode1 == inode2 && size1 == size2 && mtime1 == mtime2
 
 {- Weak comparison of the inode caches, comparing the size and mtime, but
  - not the actual inode.  Useful when inodes have changed, perhaps
@@ -54,4 +58,6 @@ instance Arbitrary InodeCache where
 		<*> arbitrary
 
 prop_read_show_inodecache :: InodeCache -> Bool
-prop_read_show_inodecache c = readInodeCache (showInodeCache c) == Just c
+prop_read_show_inodecache c = case readInodeCache (showInodeCache c) of
+	Nothing -> False
+	Just c' -> compareStrong c c'