[dmd-internals] Pulling D language enhancements

[Walter Bright via dmd-internals]

The following:

https://github.com/D-Programming-Language/dmd/pull/3907

https://github.com/D-Programming-Language/dmd/pull/3947

are both significant language changes. Language enhancements should only be 
pulled by myself. I understand that it is frustrating when I am slow to respond 
to these issues. I need to do better. But language enhancement approvals are 
still on my plate.