Allow debugger to attach to more classes of requests

Summary: Specifically any request sent with a document root never had
its sandbox setup.  This patch feels like a bit of a hack, but with
just these two lines i can attach to and debug live fcgi request
that i could not without it.

Closes https://github.com/facebook/hhvm/pull/3276

Reviewed By: @ptarjan

Differential Revision: D1457845

Pulled By: svcscm