If tickless idle mode is in use then ensure prvResetNextTaskUnblockTime() is called...

If tickless idle mode is in use then ensure prvResetNextTaskUnblockTime() is called after a task is unblocked due to a bit being set in an event group.  This allows the MCU to re-enter sleep mode at the earliest possible time (rather than waiting until the timeout that would occur had the task not being unblocked be the event group) and matches a similar change made for queues and derivative objects (semaphores, etc.) some time ago.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2796 1d2547de-c912-0410-9cb9-b8ca96c0e9e2