add --dry-run: New option

This is intended for users who want to see what it would output in order to
eg, check if a file would be added to git or the annex. It is not intended
as a way for scripts to get information.

Sponsored-by: Dartmouth College's Datalad project

Command/AddUrl.hs

@@ -476,7 +476,7 @@ addWorkTree _ addunlockedmatcher u url file key mtmp = case mtmp of
 					(fromRawFilePath file)
 					(fromRawFilePath tmp)
 				go
-			else void $ Command.Add.addSmall file s
+			else void $ Command.Add.addSmall (DryRun False) file s
   where
 	go = do
 		maybeShowJSON $ JSONChunk [("key", serializeKey key)]