Related to: #14242#14243 14293
Variants passed to LookupContext#find() seem to be ignored, so
I've used the setter instead: `finder.variants = [ variant ]`.
I've also added some more test cases for variants. Hopefully this
time passing tests will mean it actually works.
This add support for sending an explicit opt-out of the "Russian-doll"
cache digest feature on a case-by-case basis. This is useful when cache-
expiration needs to be performed manually and it would be otherwise
difficult to know the exact name of a digested cache key.
More information: https://github.com/rails/cache_digests/pull/16
