Escape the optgroup labels during initialization step.
Merge branch 'xss_fixes_from_defectify_com' of github.com:zsombor/chosen into better_text_escaping

Conflicts:
	chosen/chosen.jquery.js
	chosen/chosen.jquery.min.js
	chosen/chosen.proto.js
	chosen/chosen.proto.min.js
	coffee/lib/abstract-chosen.coffee