scm: darcs: override client_available method (#4273).

I forgot it.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4881 e93f8b46-1217-0410-a6f0-8f06a7374b81

lib/redmine/scm/adapters/darcs_adapter.rb

@@ -38,6 +38,10 @@ module Redmine
             @@client_version ||= (darcs_binary_version || [])
           end
 
+          def client_available
+            !client_version.empty?
+          end
+
           def darcs_binary_version
             darcsversion = darcs_binary_version_from_command_line
             if m = darcsversion.match(%r{\A(.*?)((\d+\.)+\d+)})