* lib/gc.h (gc_sha256, gc_sha512): New declarations.
* lib/gc-gnulib.c: Include sha256.h, sha512.h.
(MAX_DIGEST_SIZE): Set to 64.
(_gc_hash_ctx, gc_hash_open, gc_hash_digest_length, gc_hash_write,
gc_hash_read, gc_hash_buffer): Add support for sha256 and sha512.
(gc_sha256, gc_sha512): New functions.
* lib/gc-libgcrypt.c (gc_sha256, gc_sha512): New functions.
* modules/crypto/gc-sha256: New file, based on modules/crypto/gc-sha1.
* modules/crypto/gc-sha512: New file, based on modules/crypto/gc-sha1.