const?? When and why? This is ugly!

[Don]

Andrei Alexandrescu wrote:
> As far as signatures of functions in std.string, I agree that those not 
> needing a string of immutable characters should just accept in Char[] 
> (where Char is one of the three character types). That should make 
> people using mutable and immutable strings equally joyous.

Also std.conv (especially the scheduled-to-be-deprecated toInt(), etc),
and probably also the functions in std.file, such as exists().