scm: darcs: set supports_directory_revisions true at model (#7984).

Darcs adapter saves directory changes in database.
So, Redmine 1.1 shows latest changesets in sub directory.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@5478 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/repository/darcs.rb

@@ -36,6 +36,10 @@ class Repository::Darcs < Repository
     'Darcs'
   end
 
+  def supports_directory_revisions?
+    true
+  end
+
   def entry(path=nil, identifier=nil)
     patch = identifier.nil? ? nil : changesets.find_by_revision(identifier)
     scm.entry(path, patch.nil? ? nil : patch.scmid)