Fixes bandwidth_ to successfully init new installs.

Previously the script would try to divide by 0 for calculating rates
on the first run, and crash before getting to store() to write initial
values thus never initing itself. This fixes that, and makes it a
little easier to debug in case of future crashes (no need for 'eval'
wrapper).
Allows setting warnings by environment variables.
update documentation
include interface in title
need autoconf before config
Merge pull request #295 from cryptickrisp/master

Fixes plugins/network/bandwidth_ initialization for first runs