Fixing biweekly realign when used with spans option

The realign method should be working from the pure opening time without the duration shift used for the spans option.

lib/ice_cube/schedule.rb

@@ -413,7 +413,7 @@ def enumerate_occurrences(opening_time, closing_time = nil, options = {}, &block
       spans = options[:spans] == true && duration != 0
       Enumerator.new do |yielder|
         reset
-        t1 = full_required? ? start_time : realign((spans ? opening_time - duration : opening_time))
+        t1 = full_required? ? start_time : realign(opening_time) - (spans ? duration : 0)
         loop do
           break unless (t0 = next_time(t1, closing_time))
           break if closing_time && t0 > closing_time

spec/examples/weekly_rule_spec.rb

@@ -165,6 +165,16 @@ module IceCube
       ])
     end
 
+    it 'should find the next date on a biweekly sunday searching from a few days before the date' do
+      t0 = Time.utc(2017, 1, 15, 9, 0, 0)
+      t1 = Time.utc(2017, 1, 24)
+      t2 = t0 + (2 * ONE_WEEK)
+      schedule = Schedule.new(t0, :duration => IceCube::ONE_HOUR)
+      schedule.add_recurrence_rule Rule.weekly(2, :sunday).day(:sunday)
+      t3 = schedule.next_occurrence(t1, :spans => true)
+      expect(t3).to eq(t2)
+    end
+
     it 'should validate week_start input' do
       expect { Rule.weekly(2, :someday) }.to raise_error(ArgumentError)
     end