Bug 5170 - simplify i2d_PublicKey in pkey_eq

  o Code simplification and refactoring:

    - Remove contrib/id_to_fp.c since it wasn't used anywhere.

    - Since OpenSSL 0.9.7 i2d_RSAPublicKey supports allocating output buffer.

      Use this feature to avoid calling this function twice. Fixes #5170.

    - Since OpenSSL 0.9.7 i2d_* functions support allocating output

      buffer. Avoid calling twice: i2d_RSAPublicKey, i2d_DHparams,

      i2d_X509, i2d_PublicKey. Fixes #5170.

  /* We'd like to do this, but openssl 0.9.7 doesn't have it:

     return EVP_PKEY_cmp(a,b) == 1;

  */

  unsigned char *a_enc=NULL, *b_enc=NULL, *a_ptr, *b_ptr;

  int a_len1, b_len1, a_len2, b_len2, result;

  a_len1 = i2d_PublicKey(a, NULL);

  b_len1 = i2d_PublicKey(b, NULL);

  if (a_len1 != b_len1)

    return 0;

  a_ptr = a_enc = tor_malloc(a_len1);

  b_ptr = b_enc = tor_malloc(b_len1);

  a_len2 = i2d_PublicKey(a, &a_ptr);

  b_len2 = i2d_PublicKey(b, &b_ptr);

  tor_assert(a_len2 == a_len1);

  tor_assert(b_len2 == b_len1);

  result = tor_memeq(a_enc, b_enc, a_len1);

  tor_free(a_enc);

  tor_free(b_enc);

  unsigned char *a_enc = NULL, *b_enc = NULL;

  int a_len, b_len, result;

  a_len = i2d_PublicKey(a, &a_enc);

  b_len = i2d_PublicKey(b, &b_enc);

  if (a_len != b_len || a_len < 0) {

    result = 0;

  } else {

    result = tor_memeq(a_enc, b_enc, a_len);

  }

  if (a_enc)

    OPENSSL_free(a_enc);

  if (b_enc)

    OPENSSL_free(b_enc);

  return result;

}