Rollup of 9 pull requests#60834

Merged

bors merged 22 commits intorust-lang:masterfrom

Centril:rollup-fikyi9i

May 14, 2019

Commits on Apr 20, 2019

Add implementations of last in terms of next_back on a bunch of DoubleEndedIterators.
khuey
committed

Commits on May 1, 2019

Commits on May 2, 2019

clarify wording
RalfJung
committed

Commits on May 10, 2019

Allow subdirectories to be tested by x.py test
varkor
committed

Commits on May 14, 2019