Fix #2529: explicit protection package #3651

[Kagamin via Digitalmars-d-announce]

On Saturday, 23 August 2014 at 09:14:13 UTC, Dmitry Olshansky 
wrote:
> Yes, that was my initial pull. The stuff inside was marked as 
> `package`, as only package.d currently has the same public API.
>
> Then Dicebot suggested that since all modules are for the 
> moment internal they have to be moved somewhere until public 
> API is fleshed out (as it may change module name etc.).
>
> 2 options that both do NOT currently work:
> std.regex.internal
> std.internal.regex

If the user relies that a symbol is found in 
std.internal.regex.backtracking, moving it will break the code 
too. So what's the difference?