give static assert the pragma(msg,...) changes

[Nicholas Wilson]

Continuing in the vein of making error messages nicer:

Is there any reason that static assert, which deals with compile 
time messages, doesn't function the same way as pragma(msg,...), 
which also deals with compile time messages, w.r.t multiple 
arguments to the string that can be anything including types?

It just occurred to me that there is a lot of string 
concatenation and `.stringof` use.