Calendar: failing solemnity-loss integration test

refs #80

Solemnities are the only rank of celebrations guaranteed to be
celebrated every year, but due to a bug in the transfer logic on some
years one solemnity gets lost and another one scheduled twice (both on
the original date and on the date to which it was ought to be
transferred)

spec/calendar_spec.rb

@@ -476,6 +476,30 @@
         expect(celebs[0]).to eq st_none
       end
 
+      describe 'no sanctorale solemnity is lost' do
+        let(:sanctorale) { CR::Data::GENERAL_ROMAN_ENGLISH.load }
+
+        (2020..2040).each do |year|
+          it year do
+            calendar = CR::Calendar.new year, sanctorale
+
+            all_actually_celebrated = Set.new(
+              calendar
+                .each
+                .collect {|day| day.celebrations.collect &:symbol }
+                .flatten
+                .compact
+            )
+            sanctorale_solemnities =
+              sanctorale.solemnities.collect {|_,celebration| celebration.symbol }
+
+            sanctorale_solemnities.each do |sym|
+              expect(all_actually_celebrated).to include sym
+            end
+          end
+        end
+      end
+
       it 'transfer of suppressed Annunciation (real world example)' do
         c = described_class.new 2015, s