ivaynberg/select2 — pull request #2875 by pivotal-casebook (2014-12-17 20:24:51+00:00)
Title: Fix accessible aria activedescendant attribute

Remove aria-activedescendant attribute after the dropdown is closed,
to make sure the aria properties is vaild for aduit-tool

[https://code.google.com/p/accessibility-developer-tools/wiki/AuditRules#AX_ARIA_04:_ARIA_state_and_property_values_must_be_valid]