Add system and env arguments to asset tasks

The preprocess task requires system and env arguments in order to
correctly load up the django environment to preprocess sass files to
inject themes.

In order for that task to recieve the arguments, all tasks that depend
on it also have to accept that same set of arguments.

This will all go away once the next evolution of themes arrives, which
will remove the preprocessing needed to inject theme names.

rakelib/assets.rake

@@ -55,8 +55,9 @@ def sass_cmd(watch=false, debug=false)
           "#{watch ? '--watch' : '--update'} -E utf-8 #{sass_watch_paths.join(' ')}"
 end
 
+# This task takes arguments purely to pass them via dependencies to the preprocess task
 desc "Compile all assets"
-multitask :assets => 'assets:all'
+task :assets, [:system, :env] => 'assets:all'
 
 namespace :assets do
 
@@ -80,8 +81,9 @@ namespace :assets do
     {:xmodule => [:install_python_prereqs],
      :coffee => [:install_node_prereqs, :'assets:coffee:clobber'],
      :sass => [:install_ruby_prereqs, :preprocess]}.each_pair do |asset_type, prereq_tasks|
+        # This task takes arguments purely to pass them via dependencies to the preprocess task
         desc "Compile all #{asset_type} assets"
-        task asset_type => prereq_tasks do
+        task asset_type, [:system, :env] => prereq_tasks do |t, args|
             cmd = send(asset_type.to_s + "_cmd", watch=false, debug=false)
             if cmd.kind_of?(Array)
                 cmd.each {|c| sh(c)}
@@ -90,7 +92,8 @@ namespace :assets do
             end
         end
 
-        multitask :all => asset_type
+        # This task takes arguments purely to pass them via dependencies to the preprocess task
+        multitask :all, [:system, :env] => asset_type
         multitask :debug => "assets:#{asset_type}:debug"
         multitask :_watch => "assets:#{asset_type}:_watch"