vhost error_log ignored with passenger

[auxbuss]

When reopening $stderr in "a" (append) mode, the file is not written to.
However, when reopening with "w" (write) mode, things work as expected.

Also, since I have the server error log set to debug, reopening $stderr
also results in other messages being written. For example, info
messages.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,223288,223731#msg-223731