Note that it does not prevent storing p2p access tokens or multicast
encryption keys, since those are not cached; the previous commit
established the distinction.
How well this works depends on how often getRemoteCredPair is called and
how expensive it is. In some cases setting this will result in an annoying
number of gpg password prompts and/or slowdowns due to reading creds
from the git-annex branch and decrypting, which could be improved by calling
getRemoteCredPair less often.
This commit was sponsored by Ilya Shlyakhter on Patreon.
