fix preferred content check for 1 semitrusted or better copy

Let's make semitrusted+:1 mean that, since it cannot be expressed easily
with the current syntax (could use (semitrusted:1 or trusted:1), but that
does not scale to higher values than 2 copy, and also fails if I add more
trust levels).

Thanks to Andy for spotting this bug by just reading my blog.

Limit.hs

@@ -145,8 +145,8 @@ addCopies = addLimit . limitCopies
 
 limitCopies :: MkLimit
 limitCopies want = case split ":" want of
-	[v, n] -> case readTrustLevel v of
-		Just trust -> go n $ checktrust trust
+	[v, n] -> case parsetrustspec v of
+		Just pred -> go n $ checktrust pred
 		Nothing -> go n $ checkgroup v
 	[n] -> go n $ const $ return True
 	_ -> Left "bad value for copies"
@@ -160,8 +160,11 @@ limitCopies want = case split ":" want of
 		us <- filter (`S.notMember` notpresent)
 			<$> (filterM good =<< Remote.keyLocations key)
 		return $ length us >= n
-	checktrust t u = (== t) <$> lookupTrust u
+	checktrust pred u = pred <$> lookupTrust u
 	checkgroup g u = S.member g <$> lookupGroups u
+	parsetrustspec s
+		| "+" `isSuffixOf` s = (>=) <$> readTrustLevel (beginning s)
+		| otherwise = (==) <$> readTrustLevel s
 
 {- Adds a limit to skip files not believed to be present in all
  - repositories in the specified group. -}

Types/StandardGroups.hs

@@ -74,4 +74,4 @@ preferredContent UnwantedGroup = "exclude=*"
 {- Most repositories want any content that is only on untrusted
  - or dead repositories. -}
 lastResort :: String -> String
-lastResort s = "(" ++ s ++ ") or (not copies=semitrusted:1)"
+lastResort s = "(" ++ s ++ ") or (not copies=semitrusted+:1)"

doc/git-annex.mdwn

@@ -688,6 +688,9 @@ file contents are present at either of two repositories.
   copies, on remotes with the specified trust level. For example,
   "--copies=trusted:2"
 
+  To match any trust level at or higher than a given level, use
+  'trustlevel+'. For example, "--copies=semitrusted+:2"
+
 * --copies=groupname:number
 
   Matches only files that git-annex believes have the specified number of

doc/preferred_content.mdwn

@@ -88,7 +88,7 @@ any repository that can will back it up.)
 
 All content is preferred, unless it's in a "archive" directory.
 
-`(exclude=*/archive/* and exclude=archive/*) or (not copies=semitrusted:1)`
+`(exclude=*/archive/* and exclude=archive/*) or (not copies=semitrusted+:1)`
 
 ### transfer
 
@@ -100,7 +100,7 @@ USB drive used in a sneakernet.
 The preferred content expression for these causes them to get and retain
 data until all clients have a copy.
 
-`(not (inallgroup=client and copies=client:2) and exclude=*/archive/* and exclude=archive/*) or (not copies=semitrusted:1)`
+`(not (inallgroup=client and copies=client:2) and exclude=*/archive/* and exclude=archive/*) or (not copies=semitrusted+:1)`
 
 The "copies=client:2" part of the above handles the case where
 there is only one client repository. It makes a transfer repository
@@ -119,20 +119,20 @@ All content is preferred.
 Only prefers content that's not already backed up to another backup
 or incremental backup repository.
 
-`(include=* and (not copies=backup:1) and (not copies=incrementalbackup:1)) or (not copies=semitrusted:1)`
+`(include=* and (not copies=backup:1) and (not copies=incrementalbackup:1)) or (not copies=semitrusted+:1)`
 
 ### small archive
 
 Only prefers content that's located in an "archive" directory, and
 only if it's not already been archived somewhere else.
 
-`((include=*/archive/* or include=archive/*) and not (copies=archive:1 or copies=smallarchive:1)) or (not copies=semitrusted:1)`
+`((include=*/archive/* or include=archive/*) and not (copies=archive:1 or copies=smallarchive:1)) or (not copies=semitrusted+:1)`
 
 ### full archive
 
 All content is preferred, unless it's already been archived somewhere else.
 
-`(not (copies=archive:1 or copies=smallarchive:1)) or (not copies=semitrusted:1)`
+`(not (copies=archive:1 or copies=smallarchive:1)) or (not copies=semitrusted+:1)`
 
 Note that if you want to archive multiple copies (not a bad idea!),
 you should instead configure all your archive repositories with a
@@ -160,7 +160,7 @@ local copy of every file. Instead, you can manually run `git annex get`,
 Only content that is present is preferred. Content in "archive"
 directories is never preferred.
 
-`(present and exclude=*/archive/* and exclude=archive/*) or (not copies=semitrusted:1)`
+`(present and exclude=*/archive/* and exclude=archive/*) or (not copies=semitrusted+:1)`
 
 ### unwanted