Fixes Issue 5450 - Don't generate default ctor if base class lacks default ctor.
Fixes Issue 9574 - Better diagnostic on old 'alias this = that' syntax.
Merge pull request #1685 from AndrejMitrovic/Fix9574

Issue 9574 - Better diagnostic on old 'alias this = that' syntax.
Merge pull request #1439 from AndrejMitrovic/Fix5450

Issue 5450 - Don't generate default ctor if base class lacks default ctor
fix Issue 9663 - [REG2.063a] ICE caused by issue 7444 change.
Merge pull request #1727 from 9rnsr/fix9663

Issue 9663 - [REG2.063a] ICE caused by issue 7444 change.