Refactor: Reduce duplicated code in measure.rb

[GabrielLidenor]

closes #1249

Why

puts "#{added[0]} is added." was written twice in the code

Solution

private method to encapsulate the logic and prevent duplication.

[tompng]

It is added in IRB.conf[:MEASURE_CALLBACKS], so it's an internal expression of type, callback, and measuring argument, but I'm not sure if the whole tuple is really called measure_callback.
Currently, the internal structure of set_measure_callback is only leaked to here. Passing internal structure to another method will increase the leak range.

How about something like this?

# Leave unrelated part
added  = IRB.set_measure_callback(arg)
# display_added_message(type) needs type, will print a message,
# and nil-check is done in here, the caller site, not in display method.
display_added_message(added[0]) if added

[GabrielLidenor]

Thanks for the feedback.

Good to know about the leak, that makes sense to me, thanks for spending time pointing that out.

I will address that now

[GabrielLidenor]

@tompng comment addressed. Thank you once again.