Remove direct access checks

Issue: https://github.com/kohana/core/issues/508
@lenton even if nobody is using 3.4 in production yet, if you take out the check now somebody has to be sure to reorganise the project structure in future. If for whatever reason that doesn't happen before someone deploys a dev/beta branch somewhere that matters then that's a problem.

If you leave the check or switch to simple die() now it can always be changed later, but we'll not have lost any security in the interim.