Added unsetValueOption() to the Form\Element\Select and Form\Element\MultiCheckbox
Merge branch 'hotfix/1170'

Close #1170
Merge remote-tracking branch 'origin/pr/1176' into hotfix/1176

Conflicts:
	docs/languages/en/modules/zend.form.element.select.rst
Merge branch 'hotfix/1176' into develop

Forward port #1176