Fix time-of-day-related query failures

Failure running today June 6, 2016 at 10:47 am CST

```
1) RailsAdmin::Adapters::ActiveRecord #build_statement supports datetime type query
   Failure/Error: expect(abstract_model.send(:filter_scope, scope,  'datetime_field' => {'1' => {v: ['', 'February 01, 2012 00:00', 'March 01, 2012 00:00'], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field BETWEEN ? AND ?)', Time.local(2012, 2, 1), Time.local(2012, 3, 1).end_of_day]).where_values)

       expected: ["(field_tests.datetime_field BETWEEN '2012-02-01 06:00:00.000000' AND '2012-03-02 05:59:59.999999')"]
            got: ["(field_tests.datetime_field BETWEEN '2012-01-31 06:00:00.000000' AND '2012-03-01 05:59:59.999999')"]

2) RailsAdmin::AbstractModel filters on datetimes with :en locale lists elements within outbound limits
   Failure/Error: expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 03, 2012 00:00', ''], o: 'between'}}}).count).to eq(2)

        expected: 2
             got: 3
```

spec/rails_admin/abstract_model_spec.rb

@@ -50,11 +50,11 @@
       end
 
       it 'lists elements within outbound limits' do
-        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 02, 2012 00:00', 'January 03, 2012 00:00'], o: 'between'}}}).count).to eq(2)
-        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 02, 2012 00:00', 'January 02, 2012 00:00'], o: 'between'}}}).count).to eq(1)
-        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 03, 2012 00:00', ''], o: 'between'}}}).count).to eq(2)
-        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', '', 'January 02, 2012 00:00'], o: 'between'}}}).count).to eq(2)
-        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['January 02, 2012 00:00'], o: 'default'}}}).count).to eq(1)
+        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 02, 2012 12:00', 'January 03, 2012 12:00'], o: 'between'}}}).count).to eq(2)
+        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 02, 2012 12:00', 'January 02, 2012 12:00'], o: 'between'}}}).count).to eq(1)
+        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', 'January 03, 2012 12:00', ''], o: 'between'}}}).count).to eq(2)
+        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['', '', 'January 02, 2012 12:00'], o: 'between'}}}).count).to eq(2)
+        expect(@abstract_model.all(filters: {'datetime_field' => {'1' => {v: ['January 02, 2012 12:00'], o: 'default'}}}).count).to eq(1)
       end
     end
   end

spec/rails_admin/adapters/active_record_spec.rb

@@ -315,10 +315,10 @@ class PlayerWithDefaultScope < Player
 
     it 'supports datetime type query' do
       scope = FieldTest.all
-      expect(abstract_model.send(:filter_scope, scope,  'datetime_field' => {'1' => {v: ['', 'February 01, 2012 00:00', 'March 01, 2012 00:00'], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field BETWEEN ? AND ?)', Time.local(2012, 2, 1), Time.local(2012, 3, 1).end_of_day]).where_values)
-      expect(abstract_model.send(:filter_scope, scope, 'datetime_field' => {'1' => {v: ['', 'March 01, 2012 00:00', ''], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field >= ?)', Time.local(2012, 3, 1)]).where_values)
-      expect(abstract_model.send(:filter_scope, scope, 'datetime_field' => {'1' => {v: ['', '', 'February 01, 2012 00:00'], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field <= ?)', Time.local(2012, 2, 1).end_of_day]).where_values)
-      expect(abstract_model.send(:filter_scope, scope, 'datetime_field' => {'1' => {v: ['February 01, 2012 00:00'], o: 'default'}}).where_values).to eq(scope.where(['(field_tests.datetime_field BETWEEN ? AND ?)', Time.local(2012, 2, 1), Time.local(2012, 2, 1).end_of_day]).where_values)
+      expect(abstract_model.send(:filter_scope, scope,  'datetime_field' => {'1' => {v: ['', 'February 01, 2012 12:00', 'March 01, 2012 12:00'], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field BETWEEN ? AND ?)', Time.local(2012, 2, 1), Time.local(2012, 3, 1).end_of_day]).where_values)
+      expect(abstract_model.send(:filter_scope, scope, 'datetime_field' => {'1' => {v: ['', 'March 01, 2012 12:00', ''], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field >= ?)', Time.local(2012, 3, 1)]).where_values)
+      expect(abstract_model.send(:filter_scope, scope, 'datetime_field' => {'1' => {v: ['', '', 'February 01, 2012 12:00'], o: 'between'}}).where_values).to eq(scope.where(['(field_tests.datetime_field <= ?)', Time.local(2012, 2, 1).end_of_day]).where_values)
+      expect(abstract_model.send(:filter_scope, scope, 'datetime_field' => {'1' => {v: ['February 01, 2012 12:00'], o: 'default'}}).where_values).to eq(scope.where(['(field_tests.datetime_field BETWEEN ? AND ?)', Time.local(2012, 2, 1), Time.local(2012, 2, 1).end_of_day]).where_values)
     end
 
     it 'supports enum type query' do