Add C++11 const char* overloads for exception classes.

[Ed Smith-Rowland]

On 10/26/2012 10:26 AM, Paolo Carlini wrote:
> On 10/26/2012 04:11 PM, Ed Smith-Rowland wrote:
>> Committed.
> I can't find the message actually approving the patch. And personally 
> I'm a bit nervous about it.
>
> Paolo.
>
Well, the commit had failed anyway... ChangeLog out of date.

So I'll wait.

Ed