I think the fix here is for the message_handler that we pass throughout the 
code to be vhost specific, or ideally completely per-request.

In nginx you can normally set an error_log at any scope including per-location, 
and this lets you specify both what file to log to and how verbose that log 
should be: http://nginx.org/en/docs/ngx_core_module.html#error_log

In apache it's the same, but the only scopes allowed for it are "server config, 
virtual host" which means it's not per-request 
http://httpd.apache.org/docs/current/mod/core.html#errorlog  Log-level *is* 
per-request, though: http://httpd.apache.org/docs/current/mod/core.html#loglevel

This is a big change, though: we talk to the message_handler through the 
factory in tons of places, and they'd all need to switch to getting it through 
the server context or request context.

On the other hand, if we're not going to do this we might as well just rip out 
all the uses of message_handler and use the LOG macros instead, because they 
offer the same level of logging control as a per-factory message handler with 
much cleaner code.

Issue 999 has been merged into this issue.