Revised New Relic logging approach to go to file instead of stderr.

Updated the bin/heroku-php-* and bin/heroku-hhvm-* to include the
New Relic log files (there are 2 of them) in the stuff redirected to
$wait_pipe.  This approach should allow "heroku logs -t" to include
content from both the New Relic PHP Agent and Daemon logs.