Add a simple (raw) PKCS#1 padding mode

* src/cipher.h (PUBKEY_ENC_PKCS1_RAW): New.
* cipher/pubkey-util.c (_gcry_pk_util_parse_flaglist): Handle pkcs1-raw
  flag.
* cipher/pubkey-util.c (_gcry_pk_util_data_to_mpi):
  Handle s-exp like (data (flags pkcs1-raw) (value xxxxx))
* cipher/rsa-common.c (_gcry_rsa_pkcs1_encode_raw_for_sig):
  PKCS#1-encode data with embedded hash OID for signature verification.
* tests/basic.c (check_pubkey_sign): Add tests for s-exps with pkcs1-raw
  flag.

--
Allow user to specify (flags pkcs1-raw) to enable pkcs1 padding of raw
value (no hash algorithm is specified). It is up to the user to verify
that the passed value is properly formatted and includes DER-encoded
ASN OID of the used hash function.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Add an utility to calculate hashes over a set of files

* tests/gchash.c: New.

--
An utility like rhash that has the ability to calculate different hashes
over a set of files it usefull. Add gchash utility to calculate hashes
supported by libgcrypt.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>