Fixes from scala/scala repository

[julienrf]

I went through the history of the collections on the scala/scala repo, for the last year, and backported all the things that were missing in the strawman.

Fixes #214.

[julienrf]

I’m wondering what happened to https://github.com/scala/scala/pull/5664, it seems to have been reverted (https://github.com/scala/scala/commit/a11918d1053f3b0af32d7bd7fb5b75acb31724ff, https://github.com/scala/scala/commit/76babbb6728e5daf4fb95444273f6f8e0a4098d7 and https://github.com/scala/scala/commit/0365d58f62e5f21a2723365cb21636f382474805). Also, it seems that we have a similar PR (#354). What should we do about this stuff?

[lrytz]

https://github.com/scala/scala/pull/5664 was partially reverted because it was binary incompatible. We don't need to worry about that here.

[szeiger]

354 is the intended replacement for the parts in https://github.com/scala/scala/pull/5664 that had to be reverted due to binary compatibility constraints.

[julienrf]

354 is the intended replacement for the parts in scala/scala#5664

OK, so that’s fine to not have it in this PR.