revset: do less lookup during spanset.__contains__...
revset: do less lookup during spanset.__contains__
Attribute lookup is slow in python. So this version is going to be a bit
faster. This does not have a visible impact since the rest of the stack is much
slower but this shaves the yak a few extra nanometers.
Moreover the new version is more readable so it worth doing this change for code
quality purpose.
This optimisation was approved by a core python dev.