Fix failed tests in Chrome and Opera

[stevepiercy]

We need to rewrite the following tests which fail in Chrome and Opera, but succeed in Firefox.

Chrome

• test_submit_selected (deformdemo.test.Select2WidgetTests)
• test_submit_selected (deformdemo.test.Select2WidgetWithOptgroupTests)
• test_submit_selected (deformdemo.test.Select2WidgetMultipleTests)

Opera

• test_submit_date_empty (deformdemo.test.DateTimeInputWidgetTests)
• test_submit_success (deformdemo.test.DateTimeInputWidgetTests)
• test_submit_tooearly (deformdemo.test.DateTimeInputWidgetTests)
• test_submit_selected (deformdemo.test.Select2WidgetTests)
• test_submit_selected (deformdemo.test.Select2WidgetWithOptgroupTests)

See #85 (comment)