RFR: jsr166 jdk integration 2018-05

[Martin Buchholz]

I like thinking of ArrayList as just an optimized HashMap, Lua-style, and
HashMap.replaceAll also does not increment modCount, supporting our
"structural modification" position.

The thing that bothers me most about the status quo is the *inconsistency*
- between root list and subList, between default implementation and
concrete implementation, and between ArrayList and HashMap.  And there
seems to be no reason for users to expect any such inconsistency.