[Patch] Reimplment regex matcher using DFS

[Paolo Carlini]

On 07/23/2013 05:31 PM, Tim Shen wrote:
> Revised version, with _M_dfs_* moved to the class definition, PR
> testcases, and some comments on _M_dfs().
I nobody has further comments, I think this is Ok to go in now. Let's 
make sure we don't forget the various comments about optimization, 
pre-scanning, etc!

Then we should also add something (by hand, unfortunately, as I 
explained) to the audit trails of those bugs, because we want the 
original submitters to double check the fixes with their own code, get 
as much feedback as possible while we commit these improvements.

Paolo.