DIP66 1.2 (Multiple) alias this. Continuation of work.

[IgorStepanov via Digitalmars-d]

http://wiki.dlang.org/DIP66

First I want to apologize for the long absence.
I was very busy for those months and now I ready to continue the 
work.

This DIP has been approved with three clarifications:
about is-expression, about opDispatch and about "common" 
inheritance.
I've reflected those clarifications in this DIP version, and if 
it is OK, I'll start adaptation of my github PR to this DIP.