* g10/tofu.c (cross_sigs): When checking cross signatures, only
consider the signatures on the specified user id.
* tests/openpgp/tofu.scm: Add test for the above.
* tests/openpgp/tofu/cross-sigs/
  1938C3A0E4674B6C217AC0B987DB2814EC38277E-1.gpg:
  New file.
* tests/openpgp/tofu/cross-sigs/
  1938C3A0E4674B6C217AC0B987DB2814EC38277E-1.txt: New file.
* tests/openpgp/tofu/cross-sigs/
  1938C3A0E4674B6C217AC0B987DB2814EC38277E-2.gpg: New file.
* tests/openpgp/tofu/cross-sigs/
  1938C3A0E4674B6C217AC0B987DB2814EC38277E-2.txt: New file.
* tests/openpgp/tofu/cross-sigs/
  1938C3A0E4674B6C217AC0B987DB2814EC38277E-3.txt: New file.
* tests/openpgp/tofu/cross-sigs/
  1938C3A0E4674B6C217AC0B987DB2814EC38277E-secret.gpg: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-1.gpg: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-1.txt: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-2.gpg: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-2.txt: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-3.gpg: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-3.txt: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-4.gpg: New file.
* tests/openpgp/tofu/cross-sigs/
  DC463A16E42F03240D76E8BA8B48C6BD871C2247-secret.gpg: New file.
* tests/openpgp/tofu/cross-sigs/README: New file.