On Fri, May 1, 2015 at 12:02 PM Ankur Sinha <sanjay.ankur@gmail.com> wrote:
IIRC, in F21, clicking events on the calendar in the top panel used to
open up evolution in calendar mode

You remember wrongly, events were not clickable at all before GNOME 3.16. The correct action would be to open the event, however there is no API that works across calendar applications that we could use.

(or was there a button to open calendar?).

Yes, there was an "Open Calendar" button. In the redesigned calendar, clicking the event list's header (either "Events" on the current date, or the selected date)[0] does this now.