o Code simplification and refactoring:
    - Split crypto_digest.c into three parts: 1) general code that does not
      depend on either NSS or OpenSSL (stays in crypto_digest.c); 2) code that
      depends on NSS API (moved to crypto_digest_nss.c); 3) code that depends
      on OpenSSL API (moved to crypto_digest_openssl.c). Resolves ticket 29108.