Tell HipHop PHP to log errors

Summary:
HipHop won't log errors unless you set log_errors to true. This is
either on by default in Zend installations currently using phd, or
irrelevant.

http://www.php.net/manual/en/errorfunc.configuration.php#ini.log-errors

Test Plan:
Added error_log($random_number) to PhutilNiceDaemon, and launched it
using HipHop. Saw this in the log file:

Bringing daemon 'PhutilNiceDaemon' online...
a random number: 53707991
a random number: 1823619280
a random number: 1822487120
a random number: 564506024
...

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2626