Just in case someone forgets to clear the whole key.
* getkey.c (merge_selfsigs_main): Add an "if all else fails" path for
setting a single user ID primary when there are multiple set primaries all
at the same second, or no primaries set and the most recent user IDs are
at the same second, or no signed user IDs at all. This is arbitrary, but
deterministic.
* exec.h, photoid.h: Add copyright message.
