gpg: Change armor Version header to emit only the major version.

* g10/options.h (opt): Rename field no_version to emit_version.
* g10/gpg.c (main): Init opt.emit_vesion to 1.  Change --emit-version
to bump up opt.emit_version.
* g10/armor.c (armor_filter): Implement different --emit-version
values.
--

GnuPG-bug-id: 1572
Signed-off-by: Werner Koch <wk@gnupg.org>
(cherry picked from commit e951782e937ce290be0d89d83e84b3daea997587)

Resolved conflicts:
	NEWS
	g10/armor.c
	g10/gpg.c
unify formatting of fingerprints

This change introduces a common function to turn
a fingerprint into a human readable format.
display key fingerprints if offered by keyserver

This change tries to make use of complete key fingerprints if those are
offered by the consulted keyserver. If a keyserver returns the entire
fingerprint as a user id, it will be shown to the user searching the
database.
filter and verify keyserver responses

This changes introduces import functions that apply a constraining
filter to imported keys. These filters can verify the fingerprints of
the keys returned before importing them into the keyring, ensuring that
the keys fetched from the keyserver are in fact those selected by the
user beforehand.

It also prevents the accidental import of secret keys through key server
responses.