* cipher/cipher-gcm.c (do_ghash_buf): Add buffering for less than
blocksize length input and padding handling.
(_gcry_cipher_gcm_encrypt, _gcry_cipher_gcm_decrypt): Add handling
for AAD padding and check if data has already being padded.
(_gcry_cipher_gcm_authenticate): Check that AAD or data has not being
padded yet.
(_gcry_cipher_gcm_initiv): Clear padding marks.
(_gcry_cipher_gcm_tag): Add finalization and padding; Clear sensitive
data from cipher handle, since they are not used after generating tag.
* cipher/cipher-internal.h (gcry_cipher_handle): Add 'u_mode.gcm.macbuf',
'u_mode.gcm.mac_unused', 'u_mode.gcm.ghash_data_finalized' and
'u_mode.gcm.ghash_aad_finalized'.
* tests/basic.c (check_gcm_cipher): Rename to...
(_check_gcm_cipher): ...this and add handling for different buffer step
lengths; Enable per byte buffer testing.
(check_gcm_cipher): Call _check_gcm_cipher with different buffer step
sizes.