[patch] Make vector::at() assertion message more useful

[Paul Pluzhnikov]

On 8/17/13 8:10 AM, Gabriel Dos Reis wrote:

> I agree that we can't embark a significant IO library as part of a purely
> data structure components.
...
> This would be a regression, not an improvement.

A possible alternative is to make this conditional on e.g. 
__GLIBCXX_VERBOSE_ASSERT (or some such) macro.

Then people who don't care about the extra I/O library (e.g. because 
they are already paying that price), but do care about meaningful error 
messages from the field, could turn it on.

If that's still untenable for trunk, I'll proceed with a local patch on 
google/ branches instead.

Thanks,