fixed Formatter key

which should be the first word of the Formatter's
simple class name (e.g. :cost for CostFormatter)

lib/open_project/xls_export/formatters.rb

@@ -31,7 +31,7 @@ module OpenProject::XlsExport
       end
 
       def self.key
-        name = self.name.underscore
+        name = self.name.demodulize.underscore
         name[0..(name.index("_") - 1)].to_sym
       end
 

spec/patches/work_packages_controller_patch_spec.rb

@@ -60,6 +60,10 @@ describe WorkPackagesController, "rendering to xls", :type => :controller do
         column.caption =~ /time/i
       end
 
+      OpenProject::XlsExport::Formatters::CostFormatter.stub(:apply?) do |column|
+        column.caption =~ /cost/i
+      end
+
       get 'index',
         :format => 'xls',
         :project_id => work_packages.first.project_id,