drop, move, mirror: when two files have the same content, honor the max numcopies and requiredcopies

Eg, before with a .gitattributes like:

*.2 annex.numcopies=2
*.1 annex.numcopies=1

And foo.1 and foo.2 having the same content and key, git-annex drop foo.1 foo.2
would succeed, leaving just 1 copy, despite foo.2 needing 2 copies.
It dropped foo.1 first and then skipped foo.2 since its content was gone.

Now that the keys database includes locked files, this longstanding wart
can be fixed.

Sponsored-by: Noam Kremen on Patreon

Annex/Drop.hs

@@ -60,7 +60,7 @@ handleDropsFrom locs rs reason fromhere key afile si preverified runner = do
   where
 	getcopies fs = do
 		(untrusted, have) <- trustPartition UnTrusted locs
-		(numcopies, mincopies) <- getSafestNumMinCopies' key fs
+		(numcopies, mincopies) <- getSafestNumMinCopies' afile key fs
 		return (length have, numcopies, mincopies, S.fromList untrusted)
 
 	{- Check that we have enough copies still to drop the content.