I hope this patch is acceptable in something like its present form. If
so, I'll write up the documentation updates as well. (But I suspect it
may spark some discussion.)

It updates some rather outdated defaults hard-wired into GnuPG:

1. Default cipher algorithm: CAST5 -> AES256
2. Default digest algorithm: SHA1 -> SHA512
3. Default S2K hash algorithm: SHA1 -> SHA256
4. Default S2K iterations: 255 (this takes about 400ms in E2E, not

sure about GnuPG timing)

5. Modification detection codes always used.
6. Slightly increased default RSA key-size to better match RSA

key-size recommendations.

7. Display long key IDs by default. (Would a default of showing

fingerprints be acceptable to folks?)

8. (Try to) never fall back to MD5, SHA1, or RIPEMD160 unless the user

explicitly requests the use of one of these algorithms.