Respect error_reporting() in error handler

Summary:
This changes couple of things:

1. Errors are not converted to exceptions with @.
2. It respects error_reporting().
3. It doesn't pass ignored errors to listener.

Test Plan: Didn't see tons of "unable to select [4]: Interrupted system call at [Future.php:147]" in DarkConsole.

Reviewers: epriestley, nh

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4254