extension for logging server events

[Gregory Szorc]

Mozilla has been battling hg server meltdowns recently. We weren't 
satisfied with the data we were getting out of Apache and Mercurial 
itself (part of the reason is we are running 2.5.4 and don't have the 
blackbox extension since it apparently requires 2.6+).

So, I created an extension that logs "server" events to syslog [1]. As 
the docs say, it is tailored to Mozilla's needs and only currently 
targets 2.5.4. But if there is interest in adding some of these features 
to core (presumably integrated with blackbox), I could start sending 
patches when I have time.

FWIW, I think any sysadmin who does Mercurial would love more metrics 
out of Mercurial. I know there was a thread a few weeks back about 
counting pull events, etc. The data coming out of this extension can 
provide that.

[1] 
https://hg.mozilla.org/hgcustom/version-control-tools/file/default/hgext/serverlog/__init__.py