When "smart" (DMARC-aware) spoofing of From addresses was added, there

wasn't a mechanism to fully turn off the spoofing behavior. The only

options available were to enable the smart spoofing or to go back to

always spoofing. In commit 62f218d, Brian LeBlanc made an attempt at

fixing this, but it introduced some regressions in behavior, largely due

to the fact that my original design just wasn't built for a "fully

disable" option.
This change corrects that design by deprecating the old

enable_smart_spoofing option and introducing a new from_spoofing

option. This option can be in one of three modes: smart, always, or

never. The first two are equivalent to the original behavior of

enable_smart_spoofing=True/False, and the third fully disables

spoofing entirely, building a noreply address instead.
The old enable_smart_spoofing option still remains, and will take

effect if from_spoofing isn't explicitly set by the caller. It retains

the same default, always spoofing, for backwards-compatibility.

Consumers are encouraged to set a better default through the new

from_spoofing argument or the Django setting,

DJBLETS_EMAIL_FROM_SPOOFING.
At this time, the old argument will not be emitting a deprecation

notice, given how late we are into the 1.0.x series. Future releases

will begin to emit deprecation notices, and eventually remove the old

setting.

Unit tests pass.