Plugin syntax errors fail misteriously

[ralsina]

To reproduce:

1. Add a syntax error in a plugin
2. Try to run Nikola

You will get something like this:

No handlers could be found for logger "yapsy"
Error loading mako template system plugin

This happens whenever Yapsy wants to log something. Here's how it initializes logging:

# provide a default named log for package-wide use
import logging
log = logging.getLogger('yapsy')

Solution is to use logbook's logging compatibility module.