Correctly calculate size for array enumerator

[bdewater]

I don't think this is an actual problem for anybody, but if we're passing a size to to_enum it should be correct. Example:

array = ["a", "b", "c"]
drop = 1

current = array.each_with_index.drop(drop).to_enum { enumerable.size } 
current.size # 3 - wrong!
current.to_a.size # 2

new = array.each_with_index.drop(drop).to_enum { enumerable.size - drop } 
new.size # 2

[Mangara]

Good catch!

[Mangara]

Could you write a quick unreleased changelog entry for this? I like keeping the change log up-to-date, instead of having to go through everything that merged when cutting a release.