We introduced the new PRODUCTION setting in order to add a separation

between things which enable debug logging, and things which should

always be enabled (or disabled) in production vs. in the devserver. This

was done because a lot of server admins like to set DEBUG to True if

they're having some issue, and this would often cause their whole system

to break.
In Djblets, we can't guarantee that PRODUCTION will exist in the

settings object. This change makes it so we fall back to the DEBUG

setting if it's not present.

Ran unit tests.
Tried removing PRODUCTION from settings and saw that these things

  still worked.