hhvm.log.use_log_file = false doesn't send log to stderr

@JoelMarcey: here's the issue you requested on IRC.

What happens for me is that the setting

`hhvm.log.use_log_file = false`

doesn't lead to the hhvm log being printed to stderr. Running hhvm version:

`# php -v
HipHop VM 3.4.0 (rel)
Compiler: tags/HHVM-3.4.0-0-g817b3a07fc4e509ce15635dbc87778e5b3496663
Repo schema: 0e12aaa31fae66b5591f65603de50c9d62caafac
Extension API: 20140829`

Invoking as `hhvm -m server ...` (with `hhvm.server.type = fastcgi` configured in .ini).

Workaround for me for now, as suggested in IRC by Fred is to set:

`hhvm.log.use_log_file = true
hhvm.log.file = /dev/stderr`

(And just so people googling about this might find this: My use case was specifically about getting logs to stdout/stderr from hhvm fcgi for use with docker logging.)