Improve rsOtherShowing marking

Don't require the other showing to be on the same channel, just that
it's the exact same program with the same starttime.

While here, rename related methods to better reflect their actual
behaviour.

IsSameTimeslot() becomes IsSameTitleStartTimeAndChannel()

i.e. entirely different from just being the same Timeslot, end time
wasn't checked but Channel and Title had to match

IsSameProgramTimeSlot becomes IsSameTitleTimeslotAndChannel()

IsSameProgramTimeSlot() wasn't actually checking that it was the same
program, it would match a different episode of the same series.
Avoid memleak in LoadFromScheduler()