gpg: Allow for positional parameters in the passphrase prompt.

* g10/passphrase.c (passphrase_get): Replace sprintf by xasprintf.
--

Without that at least the French translation does not always work
because it requires positional parameters.  Windows for example does
not support them as they are not defined by C99 but by POSIX.
build: Print an error message if zlib is not installed.

* configure.ac (missing_zlib): New.
gpg: Need to init the trustdb for import.

* g10/trustdb.c (clear_ownertrusts): Init trustdb.

--

This was fixed in 1.4 branch in commit
23191d7851eae2217ecdac6484349849a24fd94a but was not applied to the
2.0 branch that exhibits the same problem. This is actually a hack
to fix a bug introduced with commit 2528178.

GnuPG-bug-id: 1622
gpg: Warn about (but don't fail) on scdaemon options in gpg.conf.

* g10/gpg.c: Add config options that should belong in scdaemon.conf
* g10/main.h, g10/misc.c (obsolete_scdaemon_option): New.

--

In gpg2, the following options are only relevant for scdaemon:

 reader-port
 ctapi-driver
 pcsc-driver
 disable-ccid

but in gpg1, they are options for gpg itself.

Some users of gpg1 might have these options in their
~/.gnupg/gpg.conf, which causes gpg2 to fail hard if it reads that
config file.

gpg2 should not fail hard, though giving a warning (and suggesting a
move to scdaemon.conf) seems OK.

This patch does *not* reintroduce any documentation for these options
in gpg.texi, even to indicate that they are "dummy" options, since
scdaemon.texi contains the appropriate documentation.

Debian-bug-id: 762844

Program names factored out from obsolete_scdaemon_option to make
reuse without new translations easier. -wk

This is a backport of commit 371c2b14b0347209efd23b4e54e1981a12d7aeab
with parts of 20c6da50d4f6264d26d113d7de606971f719a0ca but without those
which would change existing translated strings. -wk
gpg: Add shortcut for setting key capabilities.

* g10/keygen.c (ask_key_flags): Add shortcut '='.
* doc/help.txt (gpg.keygen.flags): New.
doc: Update the file OpenPGP

--

It should actually be completey reworked but for now I added just a
few notes.
gpg: Default to SHA-256 for all signature types on RSA keys.

* g10/main.h (DEFAULT_DIGEST_ALGO): Use SHA256 in --gnupg and SHA1 in
strict RFC or PGP modes.
* g10/sign.c (make_keysig_packet): Use DEFAULT_DIGEST_ALGO also for
RSA key signatures.
--

(Backported from commit d33246700578cddd1cb8ed8164cfbba50aba4ef3)
gpg: Avoid duplicate declaration of {no-,}sk-comments noops.

* g10/gpg.c: Cleanup argument parsing.

--

With c76117f8b0165fe5cec5e7f234f55f5a4cd7f0ab, the GnuPG 2.0.x branch
accidentally introduced a second (identical) argument parser for both
--sk-comments, and for --no-sk-comments.

This caused short versions (e.g. omitting the trailing "s", as gpgme
does) of either command to fail with:

   gpg: option "--sk-comment" is ambiguous
gpg: --compress-sigs and --compress-keys are not no-ops in 2.0

* g10/gpg.c: Cleanup argument parsing.

--

c76117f8b0165fe5cec5e7f234f55f5a4cd7f0ab mistakenly marked
compress-sigs and compress-keys as no-ops on the 2.0.x branch.

These options still have an effect on the 2.0.x branch, and the
duplicate declaration also causes the gpg argument parser to fail when
shortened versions of the option are present, like:

  gpg: option "--compress-k" is ambiguous
build: Update m4 scripts

* m4/gpg-error.m4: Update from Libgpg-error git master.
* m4/libgcrypt.m4: Update from Libgcrypt git master.
* configure.ac: Declare SYSROOT a precious variable.  Add extra error
message for library configuration mismatches.