New annex.largefiles setting, which configures which files git annex add and the assistant add to the annex.

I would have sort of liked to put this in .gitattributes, but it seems
it does not support multi-word attribute values. Also, making this a single
config setting makes it easy to only parse the expression once.

A natural next step would be to make the assistant `git add` files that
are not annex.largefiles. OTOH, I don't think `git annex add` should
`git add` such files, because git-annex command line tools are
not in the business of wrapping git command line tools.

Types/GitConfig.hs

@@ -37,6 +37,7 @@ data GitConfig = GitConfig
 	, annexAutoCommit :: Bool
 	, annexWebOptions :: [String]
 	, annexCrippledFileSystem :: Bool
+	, annexLargeFiles :: Maybe String
 	, coreSymlinks :: Bool
 	}
 
@@ -59,6 +60,7 @@ extractGitConfig r = GitConfig
 	, annexAutoCommit = getbool (annex "autocommit") True
 	, annexWebOptions = getwords (annex "web-options")
 	, annexCrippledFileSystem = getbool (annex "crippledfilesystem") False
+	, annexLargeFiles = getmaybe (annex "largefiles")
 	, coreSymlinks = getbool "core.symlinks" True
 	}
   where