module now has all logging code

Thisi makes our logging totally independent of whatever logging methods
are provided by Resque.  We use Resque.logger underneath, but the plugin
log statements now go through on interface that we control
ensure we make calls to Redis only once for logging

The log message in question needs to distinguish between "job is not
retriable" and "job IS retriable, but isn't actually being retried right
now".

We also don't want to go to Redis more than is required, so intermediate
variables to the rescue.  Also happens to straighten out that
double-negative, DeMorgan's Law-requiring `if` statement expression.