provide mechanism to abstract exception handling (collectd)

[manos]

A common pattern when writing checks with monitorlib, is to wrap all code in try/except blocks, so you can email (i.e. call collectd.warning()) unexpected tracebacks. Collectd will silently ignore these.

Anyway, it'd be great to simply pass monitorlib a function (your entire check), and have it handle this wrapping/alerting, to reduce code duplication across monitoring scripts. It's also really tricky to do.. if an exception is raised when handling an exception, e.g... so let's do this once, and do it right.