add Reactor:get_event_base()
add Reactor:get_event_base()

Reviewed By: kmafb

Differential Revision: D2323911

fb-gh-sync-id: 5e822df41dd2ae320a29d78949ab2e19974717af
shipit-source-id: 5e822df41dd2ae320a29d78949ab2e19974717af

facebook/fblualib,facebook/fblualib