gpg: Change the way v5 fingerprints are printed.

* g10/gpg.h (MAX_FORMATTED_FINGERPRINT_LEN): Increase by one.
* g10/keyid.c (format_hexfingerprint): Change v5 key formatting.

The new format are groups of 5 letters to resemble the CW speed
measurement rules. Many hams are used to such blocks from their CW
lessons. Note that there is no double blank in the middle as with the
v4 keys.

• Signed-off-by: Werner Koch <wk@gnupg.org>