restore old registerurl location tracking behavior

registerurl: When an url is claimed by a special remote other than the web,
update location tracking for that special remote.

registerurl's behavior was changed in commit
451171b7c1, apparently accidentially to not
update location tracking except for the web.

This makes registerurl followed by unregisterurl not be a no-op, when the
url happens to be claimed by a remote other than the web. It is a noop when
the url is unclaimed except by the web. I don't like the inconsistency,
and wish that registerurl and unregisterurl never updated location
tracking, which would be more in keeping with them being plumbing.

But there is the fact that it used to behave this way, and also it was
inconsistent that it updated location tracking for the web but not for
other remotes, unlike addurl. And there's an argument that the user might
not know what remote to expect to claim an url, so would be considerably in
the dark when using registerurl. (Although they have to know what content
gets downloaded, since they specify a key..)

Sponsored-By: the NIH-funded NICEMAN (ReproNim TR&D3) project

Command/RmUrl.hs

@@ -62,3 +62,7 @@ cleanup url key = do
 	forM_ [minBound..maxBound] $ \dl -> 
 		setUrlMissing key (setDownloader url dl)
 	return True
+	-- Unlike addurl, this does not update location tracking
+	-- for remotes other than the web special remote. Doing so with
+	-- a remote that git-annex can drop content from would rather
+	-- unexpectedly leave content stranded on that remote.