crypto/sha256-buffer: Add some tests. * tests/test-sha224-buffer.c: New file, based on tests/test-sha1-buffer.c. * tests/test-sha256-buffer.c: New file, based on tests/test-sha1-buffer.c. * modules/crypto/sha256-buffer-tests (Files): Add them. (Makefile.am): Compile and test test-sha224-buffer, test-sha256-buffer.